| thenobledrake |
I don't believe there ever has been any kind of official answer on this sort of thing... but here's an idea I had:
A horse is generally considered mature at about 4 years of age.
Birds of prey vary in the mature age from 2 to 5 years.
So you could say that since a hippogriff is a bird mixed with a horse that it follows a similar pattern - a particularly good example being that many breeds of horse and the bald eagle have the same maturity age and expected lifespan (4 years and 20 years respectively).