I don't think as Long Haul as being really young, age wise, even if he's a lot younger than usual. A character as old as he is who had lived straight through the war wouldn't be young, and years-conscious wise, he's older than G1-cartoon Optimus Prime! The big thing that makes him young-ISH is the fact that he's never really dealt with war before.

The way Names runs Arcee, I'd certainly put her in the "young" camp.