Mischna zu Wajikra 19:23

One who plants [a fruit tree] as a fence or to provide wood beams, it is exempt from [the law of] orlah. Rabbi Yose says: even if he said “The inward [facing part of the tree] is for food, and the outward [facing part] is for a fence,” the inward [facing part] is subject [to orlah], and the outward [facing part] is exempt.

Up until when are they called saplings? Rabbi Elazar ben Azariah says: until they are permitted for common use. But Rabbi Joshua says: until they are seven years old. Rabbi Akiba says: [the word] sapling, [it goes] according to its name. A tree which had been cut down and then produced fresh shoots: if one handbreadth or less, they are regarded as saplings, if more than a handbreadth they are regarded as trees, the words of Rabbi Shimon.

He used to say: At five years of age the study of Scripture; At ten the study of Mishnah; At thirteen subject to the commandments; At fifteen the study of Talmud; At eighteen the bridal canopy; At twenty for pursuit [of livelihood]; At thirty the peak of strength; At forty wisdom; At fifty able to give counsel; At sixty old age; At seventy fullness of years; At eighty the age of “strength”; At ninety a bent body; At one hundred, as good as dead and gone completely out of the world.