Hello

You have a very valid question. Although your weight falls in the normal range of the body Mass index (BMI) for your height. Your BMI is 20.8 which is totally healthy. It is natural for some individuals to feel that they need to gain a little extra weight for a more full appearance. Lets put one topic to rest first. That is your height. It is impossible to increase height at the age of 30 as the natural areas in the bone that grow to increase height have ossified (hardened) permanently. Some people might go for experimental risky surgeries which is not recommended at all. Therefore lets go straight to your question about weight gain. Weight can be gained in 2 ways. By gaining fat or by gaining muscle. Fat gain is not recommended or healthy as it can increase health risks in a number of ways which are out of the scope of this question. Therefore it is advisable to gain muscle mass. That will not only help you gain weight but also give you a better form and posture. So to gain muscle you need to train, like go to a gym to work out. The experts at gym can also guide you as to what you can do to gain muscle. To make things easier for you there is a simple rule what you can use to understand the types of exercises that will help you gain weight. An exercise that you can do multiple reps (repetitions) of is going to help you lose fat and lean and tighten your muscles whereas an exercise that you can do only a few reps of will help you gain muscle mass. Example being, lifting heavy weights will help you gain muscle whereas lifting lighter weights will help you lean up and lose fat. If you do start training please eat a balanced diet and extra protein according to your exercise routine. I hope this helps.