As Jan would say, 42.
Age doesn't have a lot to do with sex. It's the ability to financially, physically and mentally raise a child that determines if you're ready for sex.
An age where you clearly understand and can exercise responsibility for the consequences of your actions. So .. That could plausibly be after the ripe old age of 40!
Sex kills. Haven't you heard?
Once we are mature enough to deal with all the possible consequences on our own, every age is a good age. Some never get there, no matter how long they live.
First time---having a good experience depends on the existence of a number of factors.
After the first time---at any age.
As others have said, when you have reached an age, maturity level, and financial ability to support a child. Even if you use protection. The only 100% effective birth control is abstinence.
-First of all +18
-When you are mature enough to know about protection and it's different aspects and available science and productions.
-When you are old enough to know even when you use protection there's always a possibility of failure and you must be prepared to take the responsibility.
-So firmly, when you feel mature enough to accept the consequences of your action.
-When you be educated enough about the topic. It is very important. A rich understanding and high education about the matter helps you to not get hurt. Enjoy more and be safe. To explore more effectively and to experience more pleasant.
-Be grown enough to know you shouldn't let yourself get caught up in the heat of the hype, you shouldn't let your guard down due emotional impressions and to know only you should approach it when you are ready physically and psychologically.