Is that 8 inches from nose to end of tail or just his body? That seems small for 4-5 months of age if you're measuring the tail. That would make me think he's more like 3 months old. If so, he is about to go through a huge growth spurt so he probably won't want to slow down for another 3 months minimum. Do you know what he weighs?
You really don't want to hold back until they are over a year, thats when you start gradually. By then it will be next winter and he'll slow down by himself and think about brumating. So keep him fat and happy so he grows big and strong.
He sounds awfully cute, have you posted any pics yet?
How is he doing with his greens? Have you tried butternut?
My smaller ones like it when I hand feed them veggies, seems they eat more that way.
Not to be gross, but how are his poops? Poops tell a lot about their health and
hydration. Like a beardie health crystal ball.
Are you giving regular baths, calcium and vitamins?
Cheryl