The gemara in Succah says that a קטן can halachically receive a lulav but can't give it back. Only a גדול can do that.
That means that the difference between a גדול and קטן is that a קטן can't give, only a גדול can.
The more you give, the more of an adult you are.....:-)
[Heard from the Rebbe Shlita]