Surprisingly - not always. I knew a lab who weighed more than I and she made it till 15 or even just 16? Obviously, the owner was an obeast as well. But obviously, these are the exceptions. We had a wonderful rottweiler at the shelter where I volunteered. She got adopted, they fed her so much that she gained probably 30-40lbs (for my liking she was even a bit too chubby before). Not even a year later her heart failed while playing fetch, at the age of 6...