My Labrador is 5 months old and 60lbs, does this mean he will grow to be over 100lbs?

My lab was the biggest one in the litter being 12lbs at 6 weeks old :) Since he has grown like a weed. At my last vet visit (last 3 wk shot interval), he grew from 41 lbs to 60 lbs within a months time. I feed him purina puppy chow for large breeds. I have been told he will be very big when he grows up. He is lean and muscular, and not a huge eater like I have been told labs are lol He goes on hikes and gets at least 3 walks a day, maybe the muscle is adding more weight?