Weight gaining tips?

So I'm 200 cm tall and only 70kg. I've always been like this my whole life, which led to many embarassing sessions of being called by my PE teacher to ask me if I wasn't being properly fed at home. There was a time in which I was extremely active: I ate alot - and healthy - and I practised a ton of sports. I was in the local basketball team, which I trained at 3 times a week, I played football with my friends every day of the week, and sometimes I went for a jog.

Eventualy I dropped out of basketball. Why? Because as I advanced rank with my age, I was falling behind physically. Everyone was getting taller and bulkier, while I was just... taller.

By my 15th anniversary I weighed 60kg. 3 years passed, and I'm sad to conclude that the weight I gained is all thanks to the extra height. In fact, I stopped being active, turned into a true couch potato for over a year now, and I still weigh the same (although I'm aware sometime in my life I'll start getting fat).

So what should I do? I already eat alot, and healthy, but I'm not really motivated to work out since for years it never gave any results for me. What do?
---
Note I don't aspire to become a human balloon, I just want some muscle, because in all honesty, I look like a walking skeleton.

I'm going to assume that you have a high metabolism and because of this your body quickly digest or breaks down your food without allowing you to gain supplements such as creatine, which is in food that helps with building muscle and gaining weight. Because of your metabolism you will have to eat more than you usually eat and begin lifting weights or do workouts such as shrugs, benchpress, squats, and so on. So I suggest a high protein diet, but do not just pig out with fast food. Eat beans, chicken, steak, fish, vegetables, and fruits. I also recommend taking whey protein to put on muscle mass since it's purpose is to help with gaining mass, muscle, and strength.

Well at the food category I think I already fit there, so I'll give another go at exercise. If I don't see minimum results in a year I'll just give up

I am 5 cm taller than you Serg and I feel almost the same, however I have joined the recruitment for Emperors's Guard which will surely push my barrier of being health way on. I eat like a wild boar at home and still skinny.

I've been skinny since as far as I can remember.

So yeah, join the army, not for the sake of shooting but for sake of your mind and body. =)

I'm too tall for the army, even if I wanted, they wouldn't let me in

Plenty of good weight lifting plans out there, just choose one that sounds do-able for your schedule and stick to it.
My little brother had this problem, and he started eating a ton - like, a ton insofar as caloric content, and would just eat for a few days, and then spend an entire day just working out for one hour at a time whenever he wasn't doing something else. I don't know that he followed any plan, but he just had a gym membership and ate lots of that whey protein stuff and protein shakes. and was also really careful that he got enough nourishment from his food as well.

Dont belive that since im taller than you. You cant be "too tall" for that unless you live in north korea, lol

Just eat less healthy and cultivate mass.

A high metabolism and a tendency to build lean muscle is most likely your problem. I would suggest weight lifting. However you should not be doing 10 reps, get the weight up high enough where you can do about 3-7 only for majority of your workout. It's ok to start out lighter because you want to warm up, but definitely push yourself as far as how heavy you're lifting. I cannot, however, stress how safe you're gonna want to be. If you do this and get plenty of protein you should be fine as far as bulking up goes. Weigh yourself about every 2-3 weeks to check progress. This way you don't run down your metabolism too bad and end up gaining so much weight you end up regretting it.

Then don't believe.
Everyone is forced to go to a "national defence day" thingie at a military base when they reach 18, and they said there that every single applicant should be under 1.90m. It's even in the army's website. I don't see what reason I'd have to be lying.

No, I'm going to assume the op does not often lift or may have never lifted and doing a high weight and with low sets is a terrible idea and can seriously injure the op. When weight lifting you are supposed to work your way up involving the weight with a certain set depending on the workout. He needs to eat way more than he usually eats since he has a high metabolism and he can't properly gain lean muscle since he is most likely tall and scrawny.

Well from reading your post I gleaned two things.
1. You didn't read my entire post.
2. You don't know the difference between lean muscle/bulk muscle

I did read your post and you don't understand that lifting weights right away can cause serious injuries. I know the difference between lean muscle and bulk muscle and what the op has is neither.