With regards to the OP itself, I think it might be fine for a couple of types of magic to be tied to age, but it would be more interesting if it were sphere-based, and there were other spheres that increased in power with age (but not available to necromancers or other undead, yet would be available to elves and goblins). Having elves that lose power in some magic sphere as they age because their animus isn't pure any longer or some such might be interesting.
This would make the most sense, however, when tied to specific spheres, like say, Children, Fertility, and Youth for the blazingly obvious ones, and maybe the likes of Dawn or Strength for more metaphoric ones, while Longevity, Wisdom, and Dusk increase in power with age.
Researching Longevity magic might lead to life extensions that don't involve necromancy, for example, but require advancing into old age, first, so that it's a constant race against time to extend one's own life to have time to research the next step until one can advance the time of death past meaningful relevance or into immortality. (And it would be cool if Longevity magic might even push back the middle age brackets and such as you go, so that an old man might become apparently younger as they grow more powerful in Longevity magic.)