I'm 18 years old and I want to what's the right age to start seeing a doctor after you have your first sexual relationship.

Now. This involves anatomy that are usually skipped in routine office visits. Now that they are in service they will need periodic maintenance.You need to discuss your activity with your doc and start having pelvic exams.Males can be carriers of STD's for years without knowing it, and you don't want to risk your own fertility or health to a silent exposure.
Very Young. see a doctor right away to learn negative and positive coseqences of sexual act more neagtive ones at age 18 put your mind in education than sex, some bad diseases can occur for rest of the life.at age 18 if active learn the safty put your mind in studies not insex .