Luke is between 18 and 20.
ANH to ESB is a few years, ESB to ROTJ one.
Not much point being more specific than that; the time period is deliberately fuzzy.
Obi-Wan would appear to have been in his late fifties in ANH on the idea that TPM is 32 years earlier and he is mid-twenties in that; a consequence of GL's decision to make Qui-Gon a major character in TPM which resulted in a younger Obi-Wan.
No idea about Han, I'm afraid.