How old ARE the characters supposed to be?

When I got to the end of chapter 4, I saw the scene of Toriel and Sans having fun together. I thought that the scene was a comedic break following the heaviest part of the main route so far and while I did see some underlying conflict with Toriel's behavior, I didn't believe that it was anything too deep. After all, she is her own woman but requires her own needs after a bad divorce, and Sans was just that (be it romantic or platonic, it doesnt matter).

However when I looked online on discussions about this chapter, a good portion of the fanbase villainized Toriel as an abusive mother and Sans as a slimy opportunist. This really shocked me, because that was not how I had interpreted that scene at all. But then I realized why people thought that way and it was because they thought that the main cast was on their younger teen years, 13-14 years old, while I had always interpreted them as being a bit older at 16-17.

If you've ever been a teenager, which would scare me if you haven't, you would know that 1 teenage year is equal to about 10 full grown adult years. It really does make a world of difference if you're 14 or 16.

Now the reason why I personally believed the cast to be older mainly stems from 3 reasons:

1. It wouldn't make much sense to me personally for the college aged characters to be that much older.
2. The quick growth of some characters, mainly Susie's, made me think that they had at least some experience and maturity (although this could just be the game being set in a really small time window).
3. Thematically speaking, Deltarune makes sense to me as a coming of age story, a step for the characters into "adulthood".

It does genuinely bother me that this small detail has never been brought up though I don't think it's something super important because at the end of the day, I do think it's personal preference (even if I vastly prefer one over the other).