Is it possible to have genital herpes for years without being diagnosed by a doctor until after so long?

Yes: Herpes can lie dormant for weeks, months, years and then pop up when your body is otherwise stressed from lack of sleep, poor nutrition, another infection, or medications that make you immunocompromised.

Yes, unless you: tell your doctor, or there are active skin lesions while you are being examined, there would be no way for he/she to know.

Yes: Sometimes herpes carriers (both men and women) can be without symptoms. Asymptomatic carriers can still transmit the virus to others through intimate contact. Best wishes.