Yeah, the shortest expiration period is probably 6 years, and some schools go to 8 or 10 years. Some only care about specific courses (not all pre-reqs, but just this or that) and some will waive the time limit if you can show that you've been continuing your education ever since or have been employed in a relevant field, etc...
And a couple schools give you the option to re-take a course after a certain amount of time and have the grade replace rather than average, but it's not required - just an option.