A future version of the MC will clearly return to the past more often, proof of this is in Scarlett's box containing her memories with him, and in that box we see the flash drive that the MC (from the present) is looking for, a future version of him must have obtained the flash drive, knows it's important, and left it in the past with Scarlett for safekeeping, to then receive it back at the right time.
I don't know if I explained it well, it's all very complicated, but anyway, due to Patreon's rules, the MC isn't the father of any of the girls there, however, in an alternate timeline without those Patreon rules, he could still be the father of these girls, simply because he will continue to return to the past, so the age discrepancy is unfounded, I don't understand why you guys think this is important, he literally travels through time. ¯\_( ͠° ͟ʖ ͠°)_/¯