I don't think that it is a matter of 'sucking'. Jiu jitsu is an art with so much to learn that nobody can ever really master it. You can become proficient. You can become so well versed in it that you become the best in the world. You can understand it well enough to teach the concepts in great detail. And it takes years just to develop the basics well enough to be able to show even a bit of style.
I've been training for 4.5 years. It really takes a variety of good training partners to help to see where you personally are at. Rolling with brown belts who will let you 'try' and submit them while they calmly work on defense, big athletic spazzy white belts who require you to work hard to control them, or use more efficient technique to frustrate them and break them down without gassing, peers who started around the same time who push you while pushing themselves . . . etc.
There are a bunch of ways to grow, so it really depends on your goals. I don't know that anybody ever has that 'ah ha' moment where it all just clicks.
Sorry for the rant. To answer your question, I started when I was 31, but I was in solid shape at the time. I am/was 6' 1" 240. I'd played college football and had been lifting for a few solid years before dropping all that. I was probably deadlifting 450. So, I was pretty big and strong. I think my background in football helped with my overall balance and body awareness, but I was very average for a white belt. I always got my ass handed to me. And, as I got a bit better, I tried to apply what my instructors taught regarding using strength (which will cause you to gas). So, I would try and mentally tell myself that if I muscled out of a submission or had to use strength to gain a position/submission, that I didn't really do it right. This caused me to train differently, and I think it helped me to improve. I was also taught that I need to use my weight and that using weight to create pressure is jiu jitsu. That, I'm still struggling with.
Good luck