Good day, everyone.
I personally go with a range of +/- 5 years, while I'm restricted to -2 downwards because of law (I am 20). I think it has a lot to do with our biology and partners we find attractive. Besides all the "appearance doesn't matter" we have certain flavours, which doesn't mean we can't get a partner who doesn't suits them. For example, I go with taunt skin, so no wrinkles or such. On the other hand, I don't like to round faces, which is typical for younger people. I can't explain why, and nobody can. It's simply our likings. So, if I meet someone new, of course I will look for the appearance first and sadly I also still judge a little bit by it. But well, if a 40 year old women looks like 20 (because naturally, I hope; few is worse than desperatly trying to stay young forever), I have no problem with that. On the other case, if a 12 year old looks like 20… well, first law and second I would be worried about what the hell happened to them. But you know what I mean.
So, short version: It doesn't (or at least shouldn't) depend on the age, but more on the appearance which chance naturally with the age, but this process is individual.
For young (and for ignorant) people the age itself plays an important role sure, because you young one (yes, I'm feeling veeeeery old, not even a teen anymore) still have another point of view. Personally, I went with the thinking "Uh, they are older => they lived longer => they have more experience => they are wiser => I AM UNWORTHY!!1!"… Well, I exaggerated that one, but I think you can grab the thought. Insecurity comes with this, because "They know more than me" = "I know less". But let me tell you: Often it's not the case. Especially regarding the one or two years older acting almighty.