hello mate, dont worry about the dog its still a pup. all litter mates mature at different stages some earlier than others. you could be right your pup might of been socialised more than the new one. im having the same problem myself at moment just bought a ten month old dog pup, went out last week with a pal who has its sister and she is much more tuned in than mine, but this fella has done a lot more with his than mines previous owner. however, i know that if i, and yourself, put the time in they will come on,catch up and maybe even end up better. dont be put off mate just put the effort and