It seems hard to tell ages once you hit your mid-30s

In your 20s, ages are very distinct, and you can more or less tell the difference up until your early 30s.
But people born in '89 look like they were born in '80,
and people born in '92 look like they were born in '84.
I thought I was good at guessing ages just by looking at faces, but I guess I'm not. ㄷㄷ