I'm 20 years old and I have Gynecomastia. Is surgery is the only choice for me to correct it?

Generally by age 20 the chest has developed and if there is excess glandular tissue it is unlikely to resolve on its own.  However, if you are generally overweight you may see an improvement in the appearance of your chest area with weight loss.  If you are already at a normal body weight, you could consider seeing your primary care doctor or a plastic surgeon to learn about surgical options to change your chest appearance.

I would have to examine you to give you the best recommendation. Look at
reviews and before and after pictures as well as credentials to select
your surgeon.Kenneth Hughes, MDLos Angeles, CA

Unless you are overweight and plan on weight reduction (which only works in some not all patients), then surgery is the most predictable means to reduce male breast development. See options in below link.