I'll be 30 after Christmas (gosh, don't say 27 is too old). Anyway, I've been at one college doing A-levels for 2-years and now I'm at another doing other A-levels - the first college had a great mix of age ranges, the one I'm at now almost purely caters for 16-18 year olds and I have no mature students in any of my classes. But - the students are fantastic, doing A-levels they're motivated and smart (smarter and more interesting than most adults I know) and I am really enjoying it.
Admittedly, I haven't told them my age (they haven't asked) - so they may just think I'm 17 (brilliant).