Hello,,, you can't increase your weight as your growth plate in long bones close by 18-20years of age. What you have now is your average weight of life time.
But weight can be increased with these steps. Here are some energy-dense foods that are perfect for gaining weight:
• Nuts: Almonds, walnuts, macadamia nuts, peanuts, etc.
• Dried fruit: Raisins, dates, prunes and others.
• High-fat dairy: Whole milk, full-fat yogurt, cheese, cream.
• Fats and Oils: Extra virgin olive oil and avocado oil.
• Grains: Whole grains like oats and brown rice.
• Meat: Chicken, beef, pork, lamb, etc. Choose fattier cuts.
• Tubers: Potatoes, sweet potatoes and yams.
• Dark chocolate, avocados, peanut butter, coconut milk, granola, trail mixes. Add any of these high energy giving foods to your diet daily one or two times, and eat frequently to increase your weight.