swimmers build

Went to doctor for physical. He said that I have a classic swimmers build. I looked that term on the net and it says Good muscle tone with no bulk and low body fat. I have been working out for about 3 years and have gotten a lot stronger for instance my incline press (my fav press) is 285# x 3. The rest of my lifts are good too. I am 6'2" and 229#. Why do I have strength with no bulk?
How do I get bulk at the age of 56?

Drugs.

Food-a-Bol brotha! Nothing wrong with a swimmers body either though. Long muscles look good, and is something a lot of people actually try to achieve...