According to Mayo Clinic, Down syndrome causes a distinct facial appearance, intellectual disability, developmental delays, and may be associated with thyroid or heart disease in a person. So calling people with this syndrome 'Mongoloid' is extremely vulgar and disrespectful to ethnic Mongolians. Likewise, how will the population react if Down Syndrome was associated with 'European' looks? If you use this term, you are automatically a xenophobic, in my opinion.
If any difference is noteworthy, it would probably be that an age is usually between two times, e.g. 1290-1450AD, whereas an era is less set - but that isn't a rule, its just a matter of usage. Synonyms would be epoch, or eon. Source(s):
The Actual Age is the number of years that have passed since the structure was built. Actual age is also called the Chronological Age. The Effective Age is the estimate of the age of a structure based on its utility and physical wear and tear. The effective age is the difference between the Economic Life of the structure and the Remaining Economic Life of the structure. The appraiser considers effective age in any appraisal.