Chihuahua's Maturity?

Edna,
Pretty much he is at his full growth now. Depending on how much of a piggy he is, he may gain a pound maybe. Mainly especially with males, and if he is extremly active, he will now start gaining muscle and start toneing his body. The real key to him gaining muscle verses just a regular so-so body is plenty of exercise/play time. The more you have him fetch, the more you play tug of war, etc. all of that builds the muscles. I know cause a friend of mine took a dog from the same liter that I did, we both took boys. They were both the same size and weight at birth. But now they look totally different. Mine, Jasper, is a strapping, muscle bound, nice looking stud looking, handsome, male. Hers really looks sort of flabby, non-entergetic, and really just in looks compared to mine looks sickly in comparison. But he isn't sick.