Does one get physically stronger with age or added body weight?

I recently benched 230lbs at a ***** sporting goods just to see if I could do what they had on the bench, I'm 27 now and in the worst shape of my life I don't exercise at all. I'm pretty sure I can bench more than 230 since it was so easy to bench. The last time I tried to bench press anything was when I was 24 and use to work out and do manual labor, but then I could only max out at 180 which seems pretty pathetic for a guy that is 6'4" 260lbs at the time. Now I weight 306lbs, could it be the added on body weight, age or possibly more protein (atkins) in my diet?