Question

How much sperm does a 13 year old boy have?

Answer 1

the average for an adult is from 2 to 6 ml which is about half a teaspoon to a full teaspoon

Answer 2

There isnt an effective way to get exact numbers, given that puberty starts and ends at different time for different people, but once a males 'genitalia' starts to make sperm its not long before there's enough to fertilize a females egg.