Person (Catholic canon law)

In the canon law of the Catholic Church, a person is a subject of certain legal rights and obligations. Persons may be distinguished between physical and juridic persons. Juridic persons may be distinguished as collegial or non-collegial, and public or private juridic persons. The Holy See and the Catholic Church as such are not juridic persons, since juridic persons are created by ecclesiastical law. Rather, they are moral persons by divine law.
Physical persons.
By baptism a natural person is incorporated into the church and is constituted a person in the same. All the validly baptized, called "Christifideles", have the status of physical persons under Catholic canon law.
Age of reason.
The age of reason is the age at which children attain the use of reason and begin to have moral responsibility. On completion of the seventh year a minor is presumed to have the use of reason, but intellectual disability can prevent some individuals from ever attaining the use of reason. The term "use of reason" appears in the 1983 Code of Canon Law 17 times, but "age of reason" does not appear. However, the term "age of reason" is used in canon law commentaries such as the "New Commentary on the Code of Canon Law" published by Paulist Press in 2002.
Children who do not have the use of reason and the mentally disabled are sometimes called "innocents" because of their inability to commit sins: even if their actions are objectively sinful, they sometimes lack capacity for subjective guilt.
In the Eastern Catholic Churches, the Eucharist and Confirmation are given immediately after baptism, even to infants who do not yet have the use of reason. In Latin Rite Catholicism, Confirmation is conferred, except in danger of death, only on persons who have the use of reason; and Holy Communion may be administered to children only if "they have sufficient knowledge and careful preparation so that they understand the mystery of Christ according to their capacity and are able to receive the Body of Christ with faith and devotion." In danger of death, the Eucharist may be administered also to children who lack the use of reason, if the child can distinguish the sacrament from ordinary food and receive it reverently. This is likewise true for those who have severe intellectual disabilities such that they are not assumed ever to gain the use of reason.
Age of majority.
The age of majority in the Catholic Church is 18 following the consensus of Civil law, though, until Advent 1983, the Age of Majority was 21 in the Latin Church, based on the age of majority according to Roman Law.
Juridic persons.
In simple terms, a juridic person is an artificial construct under canon law that allows a group of persons or things to function and be treated under canon law as a single unit. The 1917 Code of Canon Law referred to all juridic persons as "moral persons", while the 1983 Code of Canon Law uses the term "moral person" solely to designate the Apostolic See and the Catholic Church itself.
A more thorough definition is given by Kennedy: "A juridic person... is an artificial person, distinct from all natural persons or material goods, constituted by competent ecclesiastical authority for an apostolic purpose, with a capacity for continuous existence and with canonical rights and duties like those of a natural person... conferred upon it by law or by the authority which constitutes it and to which it is also accountable under canon law."
The doctrine of juridic personality is thought to have its origins in canon law. It has been attributed to Pope Innocent IV, who seems at least to have helped spread the idea of "persona ficta" as it is called in Latin. In the early church, the doctrine of "persona ficta" allowed monasteries to have a legal existence that was apart from the monks, simplifying the difficulty in balancing the need for such groups to have infrastructure though the monks took vows of personal poverty. Another effect of this was that as a fictional person, a monastery could not be held guilty of delict due to not having a soul, helping to protect the organization from non-contractual obligations to surrounding communities. This effectively moved such liability to individuals acting within the organization while protecting the structure itself, since individuals were considered to have a soul and therefore capable of being guilty of negligence and excommunicated.
Canonical age.
Canonical age in Roman Catholic canon law is an age one must reach, counting from birth, when one becomes capable of incurring certain obligations, enjoying special privileges, embracing special states of life, holding office or dignity, or receiving the sacraments. 
Each of these human acts requires a development of mind, body, or spirit appropriate to its free and voluntary acceptance and an adequate knowledge of, and capacity for, the duties and obligations attached. The ages prescribed by canon law differ, as do the privileges, offices, and dignities to which they apply.
Sacraments.
From the age of seven years, all Catholics are bound to hear Holy Mass on every Sunday and every holy day of obligation. To be a sponsor in the conferring of baptism and confirmation, they have to be confirmed and normally be 16 years old (canon 874 CIC). The days of abstinence are to be respected by Catholics of at least 14 years old; the law of fasting (i.e. Ash Wednesday and Good Friday) from 18 till 59 years (canon 1252 CIC).
Priesthood, orders, and clerical office.
The ancient discipline was neither universal nor fixed, but varied with circumstances of time and locality. The requisite age, according to Gratian, for tonsure and the first three minor orders, those of doorkeeper, reader, and exorcist, was seven, and for acolyte, twelve years.
The Council of Trent fixed the ages of 21 years and 1 day for subdeaconship, 22 years and 1 day for deaconship, and 24 years and 1 day for priesthood. At present, the canon 1031 CIC fixed the ages of 23 for deaconship and 25 for priesthood. The first day of the year in which the canonical age is to be reached is sufficiently timely for the reception of the order. Trent confirmed the Lateran age of thirty years for the episcopate. The age for cardinals (including cardinal-deacons) was fixed by the Council at thirty years of age. Presently, the general age for a permanent deacon is thirty-five years of age.
No age is fixed by law for election to the papacy.
Generals, provincials, abbots, and other regular prelates having quasi-episcopal jurisdiction must, according to many, have completed their thirtieth year before election; according to others, their 25th year. Various orders and congregations, however, have their own rules for the requisite ages for inferior offices and dignities. 
The Council of Trent (Sess. xxv, cap. 7, de regular. et monial.) fixed forty years, and eight years after her profession, for an abbess, mother general, or prioress of a religious order of nuns. Could none such be found in a monastery (convent), then a nun over thirty years old and more than five years professed, can be elected. An election contrary to these rules is invalid. 
For clothing with the religious habit or entrance into the novitiate, no age is fixed by decretal law.
For religious profession, the Council of Trent prescribes sixteen years of age, with one year of novitiate. The latest enactment, prescribing simple vows for three continuous years after the novitiate before solemn profession, fixes the age for solemn profession at nineteen years for both men and women.