My oldest son was 17 lbs at 2 months old and was consistantly "off the charts" for his height and his weight. Hubby and I are both tall people.
As others have said if he has been consistently in the same range (with a few fluctuations for growth spurts) I wouldn't worry about it. But the best person to know would be your doctor. If the doctor is concerned you'll know it right away.
And while "distant" genetics can come back to haunt your child. I'd say look at yourself, your husband, siblings, parents and grandparents for a more accurate view of what is the average for your family. If being larger is part of the genetic make-up of those people then chances are ... your son will be larger too. If not, there could be an underlying problem. Or it could just be he's getting ready to go through a killer growth spurt and will even out the lbs with inches soon.
But DEFINITELY get in to see the DR asap. IF (and I'm saying very loudly IF) there is something out of the ordinary going on, it's usually best to catch it EARLY. The sooner something is found the sooner it can be treated.