Uh.. also... this point might be really overused but.. isn't Frans illegal? I mean.. look. Everyone in the game refers to Frisk as a "child" or a "kid". I have never seen any average adult be referred to names for young ages. This could mean that Frisk is indeed, a minor. Also.. Frisk can't order from Grillby's in the game, because Grillby's is a bar. Sans can, as he mentions in the game that he has a giant tab because he's too lazy to pay for all the times he has been there. The average age to drink is about 18-20 years old. Notice how Frisk was only able to get food from there with Sans? Because Sans was an adult/guardian with them, and a child needs that, especially if they're going to a place including a bar or the silly water. Frisk also doesn't order/eat anything for just adults, so this is another reason they could be a kid. My third point is the striped sweater. All the children in Undertale have striped sweaters, so this could make Frisk in the child group, as I don't see any adults with striped sweaters, like Sans. Let's move to some smaller points. Sans has a whole job, multiple ones to help him pay for him and his brother's house. Frisk and Sans are the same height, but that doesn't mean they are the same age. Sans could just have a stunted growth. Also, pedophilla is literally illegal, and I don't think Asgore would tolerate that in his castle. I also think Frisk would be smart enough not to date an older man, since they know how to flirt and date and everything. Also, if Sans is too lazy to do his job, pay his tab, and do literally anything that causes movement, then he's probably too lazy for a relationship. Thank you for coming to my Ted talk.