I'm 18, 6'2'' and 86kg / 190 lbs
5 years ago I was exactly half my weight.
My best advice in gaining weight (If you're serious) is implementing high calorie shakes / goats or coconut milk into your diet and drink lots of it! If you can get the stuff made for IBD like Modulen.
You'll soon feel a lot more energetic.
Now's the time to start exercising to reap maximal benefits, limit cardiovascular activity ie. long distance running/ slow jogging.
You want to learn the techniques fully from a personal trainer or even better, a well ripped and bulked meathead at your local gym.
I know a source who used to be in the FBI, and now is an attorney in law, who said that the FBI use barbell squats as a prime exercise to beef up their agents- this exercise is vital for weight gains!!!
5 sets of 20 reps ATG (Ass to Grass/ Deep) Squats with the heaviest weight you can handle. Search on google for correct techniques etc. or get someone knowledgable to teach you.
Other Exercises you can include:
Weighted Pullups
Weighted Dips
Bench Press
Deadlift
If you'd like better information from better qualified people, then please do yourself a favour and go to
www.rosstraining.com, the forum members are EXCELLENT in giving out training advice. Ross' books are amazing too, best in the market. In no way am I an afffiliate of this site.
My main problem is that i don't have enough calories in my diet, otherwise i'd easily be 100kg by now, but i'm working on that!
Hope this helps