How can i put on weight?

Because of your age: talk with your physician first and consider working with a nutritionist. Foods to help with healthy weight gain: almonds, cashews, pecans, sunflower seeds, flax seeds, walnuts, hummus, Avocadoes, granola, trail mix, dried fruits, extra virgin olive oil, canola oil, protein shakes, protein bars, lean meats, poultry, fish, Smoothies (with added silken tofu or powdered milk) & Greek Yogurt.