IMO, there is no such things has too young. You can't just let him sleep like an adult cause he is growing he needs his food and light. Winter arrived super early in November just after the time change and my 6 months old dragon is trying to go into winter dormancy real bad too. Hard to get her to eat. My other adult dragon has also slow down and refusing his greens.
I got some silkworms and was really happy to see that they are still going crazy over it. I also got some Repashy veggie burger and grub pie that i mix and they will eat some, most of the times. Sometime I get more lucky hand feeding them outside their vivariums. Oh and they will both eat bluberries too. you need to test different food and figure out what yours still like.
I removed all hides and keep putting Heidi back on her basking spot for 2 hours after she eat. After that I let her sleep where she want without disturbing her until next meal. I make sure she drink water from my finger and
bath her 2 x times a week instead of once.
Also when I see them with their mouth open, I quickly squeeze a piece of collar green in their mouth and they will usually eat that one piece. :lol:
I got really worried too, but I really think its the cold.