25% of the Earth's population is younger than 15. Assuming 20% of them use the internet, the TAM (not including the <15 year olds) is 80% of the world's population.
3 out of 4, or 75%, seems like nearly ever human, I'd say (though it is a matter of opinion I guess.)
Much like the cliché "the internet is the sum of all human knowledge".
If you have deep specialist knowledge in a field that has existed for more than thirty years it can become quite obvious that the internet really in is nowhere near "the sum" of our knowledge.
3 out of 4, or 75%, seems like nearly ever human, I'd say (though it is a matter of opinion I guess.)