It may surprise for your 11+ year old son to learn that in just a few years, when he is sexually mature, his testicles can produce about 1,000 sperm every second. The next question he may wonder is what happens to all of those sperm.
After the sperm have been produced in the testicles, there is a holding place for them in the epididymis. There is an epididymis attached to each testicle. The sperm mature inside the epididymis for about 2 weeks. If they are in the epididymis for longer than about 30 days, they are broken down and removed from the body. The epididymis receives these large number of sperm from the testicles every second of every day.
The only way the sperm in the epididymis can be rescued from destruction is if there is an ejaculation, The sperm are pushed into a long tube that takes them to the penis and are released during the ejaculation.
My books “I’m a Boy, Hormones!” and “I’m a Boy, How Are Girls Different?” explain this important information with very clear and simple anatomy figures to help him understand it better. I would encourage you to just give him one of the books to read. He might not be willing to have a big discussion with you about this topic, but these books explain everything he needs to know.