We don't have belts where I go and I'm 190lbs and I've only been doing jiu-jitsu for about 3 months, he claims he's been there for 3 years but he can get me into a submission and he rarely throws punches, he just pretty much lays on me while I'm trying to get out.
3 years to one person is 1 year to another. What I'm saying is it all depends on the individual's ability to learn and the effort they put into the sport.
Problem I find with a lot of big guys is they know they can "squish" us smaller guys so they stick with that and don't focus on actually learning anything. Our 340lbs. guy has been doing BJJ for over 3 years and is still a white belt. All he knows how to do is bully people to the ground with his superior size, get side control, and use the key lock to submit. When he transferred to us I had been doing BJJ for 6 months, took a 5 year layoff, and then joined back...he had been doing BJJ for 2 years to my 6 months and I was tapping him (at the time I was 250lbs.). After losing 50lbs. I had to change my game, but even though he has years on me he has never tapped me.