I don't know the reason but was told by the breeder we bought our beardie from. 1yr and younger said stay awake for brumation season. Here is my guess, since they are young and do not have a lot of body fat because of growing there is not much for them to really survive on. Once they get out of there growing stage thats when it is time to get all nice and PHAT to impress the ladies and dudes out there.