Typically, it is worthwhile to wait 2 years to see if your gynecomastia will resolve on its own. I have, however, operated on boys as young as 12 years of age because of the severity of the case and the mental stress it was causing. It does not sound like this is your situation so I would remain optimistic as most gynecomastia does resolve.
Regarding working out. Yes it may make your chest somewhat bigger. Overall, it is a much better look. Pec major muscle development makes the chest appear more masculine.