Trees start from a seed that then break the seed and gets out and grows roots that then starts making the inner layers of the tree and the bark (the outside of a tree) it then grows its leaves and creates more seeds that fall and make other trees and from then on it keeps growing larger until it can't grow no more. If you wanna know how old a tree is you can chop it down and you'll see rings if you count those rings that's how many years the tree has been growing for. Hope this helps you're little sister