Help! Im a guy whos small for my age?

I'm 18 yr old male whos small for my age. I'm very skinny and short. I'm 5'5 inches tall and weigh like 110 lbs. Im tightly muscular but im skinny so I look like one of those malnourished dudes. I To make it even better, I don't look my age. People give me years younger than I am, they say my face looks very young..wow yea can u guys help a brother out? how can i get bigger and stronger? I'm not too concerned about height I'll do what I can to get taller but weight and size is what I'm more focused on..