Few points needs to be keep in mind when you are trying for bulking:
1. You should do some exercises(min 1/2 hr) daily else you need to work harder to reduce your belly and unwanted fat in future.
2. Plan for 4-6 small meals a day rather than 2-3 big meals.
3. Eat more protein food (usually 1/1.2 gm per 1 lb of your weight) than carbs and fats that will help you to gain muscle.
To name some foods:
Eat bananas(don’t eat too many),eggs and milk on daily bases to gain weight quickly.
Eat Chicken breast ,Greens, sweet potatoes, beans, dry fruits…
Don’t eat more junk food to gain weight quickly
You have been waiting for 21 years, Take 1-2 years to get the best results.
Try to plan your diet according to how much protein your body is consuming! Our body needs 1-2 gm of protein per pound (1pound= 490gm) ! Milk, cottage cheese, chanson (sprouts), are the best source for instant protein to get better and faster results try to eat food in a breakage!!
After learning from my experience I finally understand the concept for weight gain for skinny guys. I still gain about 3–4 kg in a month despite playing football in evening for 1 hour .Eating too much really make me lazy because of full stomach and it never empty where I used to be comfortable. Someone on weight gain should not do cardio exercise but it s the time when I am with friends,someone who follow my diet will easily gain 5 kgs in a month if no cardio exercises are done..Eating in beginning is very difficult, my stomach cannot take anymore after eating my daily food, but pushing extra couple of roti in mouth is what I learn in beginning weeks .Your stomach will be stretch after sometime. And not take water before and after 30 minutes of eating.