I think anything anyone tells you is basically just that..a pure guess. Mandie was 4 lbs at 5 months and at 11 months, she is now 5.4 lbs. She'll probably end up being around 5 1/2 to 6 lbs for her adult life. I would venture a guess on yours and say that maybe he had a growth spurt earlier rather than later and will be around 10 lbs (ish). Who knows? I think it's great!
And, welcome to YT!! Hope you stick around. Would love to see more pics of your baby - by the way LOVE his name!!!