Well it used to be normal for 13 year olds to get married, provide for their family, go to war. That is historic fact. On the other hand fantasy setting usually presents higher quality of life which partly negates this historic fact. I personally think that 15 year old could do all mentioned above in regular fantasy world.
I dont know where is appeal. I have seen children characters on servers where DM team expected players to have some common sense about it. But it ended up usually with kid not even being 15 and yet having 15+ lvls and using all of its perks
. On the other hand I used to play in "arabian" (nomadic) family, where eventually children "appeared" and it was kinda fun when once in a while someone logged on as one of the children in the family and trolled us the whole evening which children like question.
"Uncle Ali?" (my character Ali, wizard)
"Yes, Rany?"
"Why is aunt Alice so poorly dressed like those ladies in town that throws themselves at all the guys?" (Alice was family friend, sorceress who used to dress... well like a courtesan)
"Well, she likes to show how pretty she is and how fearless she is because of the magic"
"Uncle Ali?"
"Yes?"
"Why do you wear so much clothes? You are best mage in the world, you should go just in your underwear to show your magic"
"Ehmmmm.... your aunt doesnt like me going out like that, so I wear lot of clothes. Just like your mother teaches you."
"Uncle Ali?"
... (rant going on like this for 10 more minutes till we safely moved from town A to town B) ...
Eventually when those children reached 15+ they became full played PC and were switched with their parents PC (= players who used to play their parents became children.. for lack of people and other issues).