How can I gain weight?

I'm 6'2" and 17, I weigh 8.5 stone (119 pounds) and feel quite skinny. I don't look like alot of skinny people but my body and face are slightly skinnier than normal, it runs in my family that it's hard for us to put on weight because we are naturally skinny until we hit near the 40 YO zone and we burn it off quite quickly but I want to get to 10 stone as soon as possible to have a healthier complexetion and have a a better built body. Is there a way for me to put on weight, I'm eating enough to maintain my weight and also I am starting to do some muscle exercises such as using dumbbells but how can I put on weight quickly and easily.