Family descendants?

If everyone reproduced at 15 you could watch the whole tribe grow up and only be 75 when your great great, great grandchild was born. But you'd likely be exhausted because someone would have to support all those babies making babies!

i think its possible, and ive known people like that

It is possible, especially if each generation has children fairly young. Example if each generation had children at 18 you would be 90 when your great great grandchildren were born and 108 when great great great grandchildren were born.