The age of sex begin right after the creation of Adam & Eve.
For us, the age of sex begin when when we came to leagal age.

The time of life when a person becomes qualified to assume certain civil and personal rights and responsibilities, usually at 18 or 21 years; legal age: under age; of age.

A period in the history of humankind marked by a distinctive characteristic or achievement: the Stone Age; the computer age.


You might want to ask. "what is the computer age?"