All depends on where you think one age ends and another begins. I use 18 to 35 for young adult and 36 to 65 for adult since most people I know in their 60s are not EA's definition of elder. Not even sure anyone under 70 fits that definition. For me, Adulthood is longer than young adulthood.
This thesaurus page is about all possible synonyms, equivalent, same meaning and similar words for the term cheeky. Princeton's WordNet(0.00 / 0 votes)Rate these synonyms: brash, cheeky, nervy(adj) offensively bold. Synonyms: cheeky, brash, jumpy, highly strung, nervy, uptight, high-strung, restive, jittery, edgy, overstrung.
Jimmy always seems to have a will of his own. mischievous (of a person, animal, or their behavior) causing or showing a fondness for causing trouble in a playful way. Your usage of cheeky is perfectly correct. The NOAD definition aptly captures your intended meaning: cheeky. impudent or irreverent, typically in an endearing or amusing way. Unfortunately, this word is not too common among American speakers.