30 year olds used to look more middle aged because of how they dressed, how they had their hair etc. It used to be the fashion for women to have shorter hair which looks ageing on most people, whereas now most women have longer hair which does make most look younger.
Women also tended to ‘grow up’ younger and move out, get married and have children at a younger age. The fashion for women of their age was different to how it is now, with 30 year olds now wearing the same thing as 20 year olds.
My impression of the past is 30 year olds used to dress the same as 50 year olds. That’s not the case today.