I'm going through this right now. I graduated in 1997, so all my classes are 10+ yrs old. Most schools are mainly concerned about the science courses, especially organic. As the others stated, the policy varies b/t schools so you will have to contact each of them. Most schools prefer applicants with classes no older than 5 yrs and you should assume this everywhere. Others like MCPHS and Pacific, have limits of 10 and 7 years respectively.
What have you been doing during the intervening years? It's important to have been involved with science for the admission committee to grant waivers. In my case, i did a lot of molecular bio/protein expression at a biotech, then worked for an engineering company transferring various biological assays to automation, and now doing oncology clinical research. So, get your resume ready to hand out to everyone... it will go a long way.
When contacting these schools have your:
1) Unofficial transcripts for every school
2) Resume
3) Course descriptions for every class (it can also be links to online catalogs)- this allows them to see what was covered in classes and if you have syllabi (which i don't) that is even better. Some schools (UCSF) will go to that level of course review to determine if your classes were good enough to begin with.
Also, be prepared to retake some classes. Even though i did well in all my classes, i'm looking to retake organic + lab this fall/spring and taking both semesters of anatomy/physiology + lab this summer. It shows them your seriousness and willingness to jump through all the hoops to get in. It just