Hi! I think your your rat would love to have a friend. Someone else with boy ratties might be able to help you better on what age boy would be best to introduce your guy too, but dont forget about quarantine. There is a sticky about it if you have not already checked it out.
My big boy rat Addo is very friendly and big and fat, and he was by himself for a couple of months.
I got him a friend, Edgar, and it took them a while to get used to each other! But as long as you do it right (read the thread about introductions like I did), they'll more than likely get along great! Rats love ratty company, as well as human company.