When is a prereq (Biology/Chemistry/Physic s) too old that you will need to retake it?
Some schools specify their expiration, but I think 5-7 years is a good indicator that you need to retake.
Ditto what Meg said, especially for biology. Chemistry and physics haven’t changed much and sometimes schools will let those slide. Another consideration is whether or not you have taken any upper level courses recently. If you have taken upper level science courses recently and done well, many schools will not care as much about the age of the pre-reqs.
It seems like we hear a lot of different experiences about this. I agree with Amy, even if your coursework is only five years old you will be smart to take another bio course to show that you’re up to speed. Bio just keeps changing so fast.
The bottom line is you’ll need to try and find out from the schools where you’d like to apply. They may be a little cagey about it, saying ‘it depends,’ or ‘we don’t have a set deadline,’ in which case you’ll need to use common sense and err on the side of taking more coursework rather than less.
Mary
posting like crazy (but now I’m done) 'cause I like my new avatar, Go Hokies! 
Thank you!
Kris
Also, you are competing for a spot with folks that DO have recent pre-reqs…so not only is it about what has changed in the material but about making yourself more competitive. The pre-reqs, specifically organic chemistry are the courses that may get more scrutinity from adcoms…