Section 3-6 MINIMUN DRIVER LICENSE REQUIREMENTS-
To secure and mantain a NASCAR Competitor license as a race driver, a NASCAR member at a minimun must:
(1) Be at least 18 years of age.
(2) If requested by NASCAR Officials, submit to and pass driving ability tests conducted by and at the descretion of NASCAR Officials, whose decision as to the applicant's driving ability is final and binding on the applicant.
(3) Be physically fit as determined in the sole discretion of NASCAR. In that regard, NASCAR may require a Competitor or applicant to submit to and pass one or more physical examinations by a qualified physician(s).
(4) Execute and deliver to NASCAR such authorizations, releases, applications, consents, waivers, resumes and other documents as may be required by NASCAR from time to time.
The above requirements are from the 2003 Grand National rulebook; the latest edition that I have handy here at home.