It was 7 years a while back, but processing times are only getting longer unfortunately. As @Dashinka said, currently the Visa Bulletin date for the F1 category is March 2016, so 8 years ahead of your Priority Date.
But if you go back in time and look (for example) at March 2020, you’ll see that the date then was October 2013, so it’s only moved forward 2.5 years in the past 5 years.
So I’d assume at least 10 years, possibly much more though, but just keep an eye on it and check to see how it’s moving every so often. And if your son/daughter wants to move sooner, then it might be worth them exploring other visa routes i.e. getting a good degree and a masters, some specialist work experience, then employment based visas maybe?
Best of luck.