I don't really recall aging effects being outlined in the Pathfinder rules, but I certainly wouldn't allow those effects to bring about any increases in maturity like mental score bonuses or age adjustments for dragons. I also don't recall anything special about old vampires being powerful, except it may be a wee bit more likely for a vampire that has actually lived 300 years to attain level 20... all this sounds more like a 1e game than a Pathfinder game.
As a DM, I don't feel constrained to create monsters that follow the books. For instance, maybe not all vampires have the traditional weaknesses, but have different ones instead (those are all over the place in literature). It would need to be established early on, though, or it WILL seem like an arbitrary effect.
I think the vampire weaknesses are deliberately stated in a way that encourages out-of-box thinking to solve the problem, and those solutions tend to be hard to apply rules to.