You should get a girlfriend whenever you feel you are ready for a real relationship with a girl. But personally, I'd say at least 16 years old is good for having girlfriends/boyfriends.
Chat with our AI personalities
Whenever your parents allow it. If they do not allow you to have a girlfriend for whatever reason, then the asnwer would be as soon as you move out of their house. (I do my best not to condone kids disobeying their parents so sneaking around is not the answer.)