Some background statistics based on the book "Sperm Wars" by Robin Baker, University of Manchester.
On average a man between puberty (I suggest age 15 y) and 30 years produces 300 million sperm/day (300,000,000).
On average a man between 30 y and 50 years produces 230 million sperm/day (230,000,000)
On average a man between 50 and 75 years produces 50 million sperm/day (50,000,000)
The last two sperm/day numbers were calculated as follows:
At age 50 years the average man produces 175 million/day -- so averaging 300 million/day and 175 million/day you get 230 million/day.
At age 70 years the average man produces 20 million/day -- so I could average 175 million and 20 million, but to be on the safe side I decreased it to 50 million/day (keeping my results on the conservative side -- I will round lower for the calculations that follow).
Each sperm has a unique set of DNA.
These sperm will appear in intercourse, masturbation, nocturnal emission. They all have to go somewhere.
On average 2 to 3 offspring survive that will reproduce. This average seems to be fairly constant in modern societies, agricultural societies and in hunter-gatherer societies. So, for all generations it hovers around 2 to 3 reproducing survivors. On average, 2 to 3 sperm will result in the fertilization of eggs that results in 2 or 3 reproducing individuals -- the rest of the sperm are doomed.
Kind of sperm:
An average man produces 3 kind of sperm:
(1) Killer Sperm constitute about 83% of all the sperm -- these are sperm that attack any sperm from another man that may be in the woman. These sperm carry a lethal dose of poison in their head, seek out foreign sperm and inject it with this poison, killing it. Apparently after a few injections the Killer Sperm has spent all it's energy and also dies.
(2) Blocker Sperm constitute about 16% of all the sperm -- these try to block entrances and storage places so that any sperm from another man cannot reach the woman's egg.
(3) Egg Getter Sperm constitute about1% of all the sperm -- these are the sperm that can possibly fertilize the woman's egg if they ever get there.
So 99% of sperm make war on other men's sperm to annihilate them so that they won't fertilize the woman's egg, and 1% have the potential to fertilize the woman's egg.