birthday calculation

It must be late, because I cannot seem to figure this out. I've got a
field which has a user's birthday - I want to figure out how old they
are in terms of years.

If I just do something like:

select current_date - user.bday;

I get their age in days, which doesn't let me take leap years into
account. Is there a simple magic date_diff function that I'm missing? Or
lacking that some other way to get postgres to do the date calculations?