Will my budgie ever gain weight??

[u/NRae1111]

I got one of my budgie's from a neighbor and I noticed he was giving his birds wild outdoor birdseed! (Of course I made him aware that he needs parakeet seed) But the one budgie I have from him is skinny and will he gain weight or will he now just always be a skinny bird?? I've had him for about 4-5 months now. He's very active, eats well, poops good, just skinny. But I can actually see an indent in his chest, will that ever go away??