The MC is 20, then Ashley is 18 and Veronica is 21. It was mentioned that Veronica is one year older than the MC, indeed it wasn't mentioned that Veronica is 21, but if you do a wee bit of math you will come to the conclusion that 20 + 1 is in fact 21! ( ͡° ͜ʖ ͡°) This would make Claire either in her late 30s or early 40s, but this isn't mentioned.
I wanted Veronica to be 19, not 18. There's this 1 year difference again but will ultimately change the role Veronica plays, since Ashley and Veronica are clearly not twins and it's not realistic to conceive another child in the same year you had one.
Also, imagining it makes it feel hollow since it's not true in the game. Hope that puts aside any follow-up suggestions to handle the problem alternatively. It is unfortunately not possible to change the ages in the mapping.xml, since it's simply part of the text instead of a label. To change it, I'd need to unpack the game and change the text, which is just a tiresome hassle that I have no intention of doing. So I've concluded to simply let it be. Maybe somebody else will be less of a lazy lizard like I am and create a mod that allows us to do this, but I have my doubts