The immediate joke responses are weird. There are healthy relationships with age gaps that have serious conversations before anything happens (and often are queer relationships tbh), but it seems like the people that make the jokes have no experience with this or have some stuff to work out personally.
I don’t ever think of partners in a numerical way. When the time and situation is right, I guess my number goes up. I haven’t had too many and am happy sharing intimacy/my life in a selective way. I’m also monogamous which influences how often this happens with someone new.