adult, grownup - a fully developed person from maturity onward

antediluvian - a very old (or old fashioned) person

centenarian - someone who is at least 100 years old

curmudgeon - a crusty irascible cantankerous old person full of stubborn ideas

dodderer - one who dodders from old age and weakness

dodo, fogey, fogy, fossil - someone whose style is out of fashion

dotard - an oldster in his dotage; someone whose age has impaired his intellect

back-number, has-been - someone who is no longer popular

nonagenarian - someone whose age is in the nineties

octogenarian - someone whose age is in the eighties

old boy - a vivacious elderly man

graybeard, greybeard, old man, Methuselah - a man who is very old

old woman - a woman who is old

septuagenarian - someone whose age is in the seventies

sexagenarian - someone whose age is in the sixties