While Akantor's answer may be good at surface level, it leaves much to be desired.
Ash's dad cannot be Red, mostly because the game and the anime are not connected and/or in the same universe, and even if they were connected via the Multiverse Theory (as I and GrimeTime, who back in the day was known as Astro, analized in this question) Red couldn't be Ash father for the following simple reasons:
• Brock and Misty, whom Red defeated during the games, have yet to age in the slightest by the time Ash meets them.
And even if we take into account the fact that people don't age in the anime, keep in mind that's a prerogative exclusive of Ash (as I also explain in this answer) due to a marcheting necessity.
• Also, Red and Ash are (and you have to not jump at me on this one, cause I know what I'm about to say will piss a lot of people off) the same person.
As in counterparts. Just as Gary and Green/Blue are the same person.
There wouldn't be a reason to have Red as Ash father if they would have the same rivals, they would just make Red the protagonist instead.
• And come on, what are the chances of literally no one ever mentioning your father being one of the greatest trainers in the world, which just so happens to come from the same town you are coming from, have the same yellow mouse you have, had beaten two of the people you spent around a year with (with them not even mentioning him ever), and being the pupil and a close friend of the man who, by coincidence, started your pokémon journey and who is now most likely spending most of his days in the same house your mother, and by reasoning his pupil's wife, lives in.
There are a lot of candidates fathers for Ash, but while Red is a fan's favorite, it's also the most unlikely.
By the way, TheJWittz made a video on this topic which you'll definitely find interesting.
I highly recommend you to watch it.
The guy he brings up as Ash's father would most likely fit into the anime's canon, but I won't spoil the surprise ;)
Hope this helped you somehow!