Like Marina said, there is no real age that one is ready for any kind of relationship.
Obviously, a five-year-old is not old enough for any kind of meaningful relationship with anyone besides their parents.
Realistically, I think that there is still some meaning to the “sweet 16” birthday party, where 16 is around the age of maturity for a real relationship. I don’t believe that age is a concrete number, however.
Honestly, I have walked through schools to see far too many 14-year-olds dry humping each other against the lockers. It did not look like a real relationship the way the guy was going after her, however. It seemed far too forced. My advice is to be careful with the way you approach any relationship. Don’t force yourself to be in a relationship for the sake of the relationship itself. Instead, the age of a person’s maturity comes when the relationship is solely about the significant other, rather than the allure of the relationship.
You will know that you are old enough when you feel as though the word ”relationship” does not matter, so long as you are with the other.