What kind of male dog is he?

He is 6 months old and weighs about 70lbs already...hes muscular and really really strong and has quite abit of loose skin yet. He hardly barks unless hes ready to come in from potty or when we do our "speak!" trick telling him to but he opens his mouth like hes trying to bark but nothing comes out. Its actially cute to witness....bless his heart! Hes very energetic with our other boxer thats 8 months old but when they quiet down and he just gets up to drink or eat he kinda walks as what we refer to as a grandpa walk kinda scoots his feet along. Do you know what kind of other breed he can be other than a boxer in which i was told from a lady i bought him from at a flea market...apparently she gets all diff kinds if dogs from somewhere and sells them so i hapened to find him. When i got him from her i was given papers stating that he was full blooded boxer and stated his parents names and that they are as well full boxers,,i also got a paper about his first shots and another for if i decided to geg him registered in which i havent done. Can anyone help. I can send a pic or two if needed. Thanks a bunch!