New 4 month old dragon is too small for his age

[Nero]

I don’t really interact with this forum but I need some help. I received a 4 month (possibly 4 month) bearded dragon from a petco that was going to put him down. He’s looks like he hatched a couple of weeks ago and he’s too small. However he moves, eats, and poops. I’m housing him in a 5 1/2 gal tank for a bit. I’ve heard moving them into big spaces early stresses them out, I have a 50 gal in storage he can live in later. I have lighting and a setup already and I’m about to go get some food for his size. He’s also very skinny and his siblings were much bigger than him. Is there anything I can give him to help?

 

[Nero]

Here’s a picture.

 

[Sadie]

Here’s a picture.

Lack of correct uvb and surface basking temps are usually the cause- please move him to a bigger tank the 50 gallon is fine section it off in 1/2 - that small of a tank he's in is to small and we need to set up a good surface basking temp- 105-110 for him taken w/ a digital probe thermometer- next a 24" Zoo Med fixture-- I want you to use the 5.0 bulb that comes w/ that fixture it will be used till you get the tank opened up completely - which won't be too long- but we need him eating a good diet of dubia roaches some nutri grubs and salads- your not going to get good temps you need or the uvb you need on that 5 1/2 gallon tank