My assumption is that with 30 age really becomes visible. It was at this age, people- the same sort of people i would hang around with and goof with- started to refer to me as "Mr." - as if by having the first grey hair- you somehow become some authoritative figure to be afraid of. Which is ridiculosis - but you cant change what people think when they see you for the first time.
I find how I dress and hold myself signals "age" more than my actual aging. If you act tired and old, no matter your age, it is a signal.
We also have hair dye, dentures, plastic surgery for those that care. And many do.
Youth is a verb.