Five years to do the degree after you have gained the necessary A Levels or equivalent. So the earliest age most people would qualify as a vet is 23, a mechanic can qualify after a two year course starting at 16 and become a MOT test at 22. Of course he has been working full time from the age of 18 (or she, I know there are female mechanics and vets).
Two year apprenticeship for a mechanic, 7 years of study for a vet.