If it helps... Almost every generation feels this way in their 20s & early 30s.
It's a psychological thing in PART (the whole mortality thing + aging thing/aka you and your friends actually ARE getting older so you're noticing things that have been coming OB for awhile)...
Part of it is also a fashion thing (the current style adds 10 years, and only looks good on teens... Choppy lengths, garish colors, bold patterns, etc. combine to make most people's skin look bad, bodies look wider and shorter, hair look older, etc. as a visual artist I HATE this style. Everyone will look younger as soon as long clean lines, better colors, and glossy hair comes back on vogue)
Part of it is an honesty thing. People GRIPE about these changed in public in their 20s & early 30s, but have come up with working solutions by 30s & 40s
Part of it is money, by later 30s & 40s, most people have more money and time to take care of themselves.
Part of it is kids at ANY age. Young children are exhausting, and expensive. Moms of 20yos often look younger than moms of 3yos
But a BIG part is the first. You know people griping about turning 30? It's because that's right about when most people start feeling old, and their friends start looking 'old'. They DON'T, as any 40yo will laugh at you... But in you mid to late 20s... Most people stop looking like kids. They've got some grey, some hair loss, some fine lines, skin that doesn't have growth hormones making it look like a teens/kids, bone are done growing, waistlines are expanding. They don't look old to anyone ELSE but they look old to themselves.