To the OP:
Yes, it is definitely the case that grades do 'expire' as far as some veterinary schools are concerned.
I am currently 32 years old, and will be 33 when I apply next year. I completed my undergrad pre-reqs an age ago (between 1997-2001). Since graduating, I have been continually employed in the animal science industry (in technical, scientific positions) to present day. That being the case, I don't think that it's useful (or in my best interest) to retake General Biology, Organic Chemistry, and the like- I just don't see much point. I have the same study skills that I did back then (and also completed an advanced degree in the interim), and have complete confidence that I can handle the rigors of a vet school curriculum.
Next year, I will be applying to four schools which do not enforce a 'pre-req expiration' clause. These are: Utah State/WSU, UC Davis, NC State, and Purdue. I am currently a resident of UT, so admission to USU/WSU is my first choice and best chance of admission. It's a very long shot for me to be accepted OOS to UC Davis, and also a long shot for acceptance to Purdue and NCSU given my residency status.
As far as retaking pre-req courses go, that's a choice only you can make. By doing so, you'll make yourself 'eligible' for admission to a far greater number of vet schools country wide. I myself would have added Auburn to my list should they not have had an expiration clause. Auburn recently bumped up its OOS admission to 30 seats per year- that's a significant number, giving an OOS applicant a decent chance of admission. Compare that with UC Davis which only takes 5-8 OOS students per year, or NC State which only accepts 18 OOS students per cycle. Purdue is a bit more generous with its OOS admissions policy.
I'm a firm believer in applying to and attending a veterinary school that will admit you. ALL vet schools are high caliber institutions, and all of them will award you a DVM degree upon completion of the program. The DVM curriculum prepares you to be an entry level, general practitioner upon graduation. That being the case, any vet school will prepare you for an entry level job in the field, and any vet school will prepare you to obtain a residency/internship in your desired field of interest. The rest of the job is up to you as a student- the student needs to put in the time/effort and make the connections to get involved with the field of 'their dreams.'
Given my professional background in the hard sciences, I have chosen not to retake 'expired' pre-req classes. The CORE emphasis of general bio, general chem, organic, analytical writing, biochemistry, etc. has not changed significantly in the past 10 years. Sure, specifics have advanced significantly- I know that as a scientist myself. Remember that the information you read in a current textbook is already 10 years old at the time of publication.
If there's a specific school to which you intend to apply that requires that your pre-reqs be completed within a specific span of time (there are many- typically the expiration window is from 5-10 years), then you really don't have much of a choice other than to retake your pre-reqs. Some schools (I'll cite UPenn here because I contacted admissions on this very issue) don't have a formal policy outlined in the admissions brochure, but do expect courses to be current (i.e. it would be a black mark against you to not have current pre-req classes). Just FYI- Tufts Univ. in MA does not have a pre-req expiration date, in addition to the schools I listed above.
Hope that this point of view is helpful, and gives you some food for thought. As someone who is a bit older, and completed your pre-reqs a while ago, please remember that you've got loads to offer a vet school as far as diversity of life experience goes. In my opinion, that could be more beneficial to you and the school than retaking pre-req courses.
Best of luck/success!
