samrosemodblog:

Oh, you mean inspiration wise as opposed to ‘why not just go with whatever everyone knows’.

Because I feel like ponies live in a medieval-esque society with magic giving them a lot of modern conveniences. As such their society is still somewhat primitive, but also fairly modern. 

And since the objective of public school is to give everyone just enough knowledge that they’ll be able to be productive members of society, ponies impart all the knowledge they need by the age of 15. This is also the average age where most ponies have their cutiemarks by now (rare exceptions to this) as well as stallions being physically grown enough for field labor and mares at a safe-enough age to be bearing foals (especially since it takes 11 months for pregnancy). And the average pony lifespan in Motherly is around 40-100 (varying with race, pegasi having the shortest average lifespan and unicorns having the hightest.)

So all those factors combined with education and the need for an active work force has the law consider ponies adults at 15, thus giving them full rights of consent.

It’s all about the universe building. I imagine in a couple hundred years that the age will be pushed up to 16 and 18 respectively, especially as the length of pony lives increases as well. But for now it’s 15.

In sparta, 15 is adult