The Disney script says Anna is 18 and Elsa 21. However, in the movie, Anna and Elsa clearly act much younger and less mature than being adults - on one hand, this could be due to their isolation, but on the other hand, if Elsa was 15 when her parents died then it's easier to explain the 3-year wait until her coronation. (Norway's age of majority is 18.) Also, if Anna was 15 years old it would explain a lot of her impulsive and reckless behavior (teenage hormones). So… what if Anna and Elsa had been 1-3 years younger during the movie?

So here's Prompt Idea #7:

AU in which Anna and Elsa are 1-3 years younger at the time of Elsa's coronation (still 3 years between parents' death and coronation). Elsa would normally refuse Anna's romantic advances for reasons we already know, but now she has one additional reason - Anna isn't old enough! ("you don't know what you're doing!")

This opens up possible story lines with Anna (age 15-17, post-coronation) trying to persuade Elsa that she is mature enough to make such a decision (which she probably isn't, unless [or especially if!] she spends a lot of time with Kristoff and the trolls), such as:

option 7a - Anna agrees to wait until she's 18 before deciding anything, outgrows her teenaged fantasies and achieves a normal and happy marriage, much to Elsa's relief (here, Elsa is the closest to a mother figure since their parents died 3 years before Elsa's coronation)

option 7b - Anna agrees to wait until she's 18 before deciding anything, outgrows her teenaged fantasies and achieves a normal and happy marriage, much to Elsa's disappointment because Elsa now has to hide her un-sisterly feelings forever.

option 7c - Anna is indeed not mature yet, falls for a series of other men/women, gets in trouble, breaks Elsa's heart, and learns her lessons the hard way as she grows up. Eventually, an older and wiser Anna finally figures out what she really wants out of life and settles down with a nice prince/commoner/whatever (possibly Kristoff)

option 7d - Same as option 7c, except that after all her hard-earned life experience and many breakups, Anna decides that Elsa really is the one for her after all - much to Elsa's consternation, because Elsa doesn't feel the same attraction and was hoping Anna would give up her teenage fantasy when she grew up!

option 7e - same as option 7d, except that Elsa does reciprocate the attraction and the two sisters live happily ever after (or, until they are exposed and executed for their perversions)

option 7f - Being both a teenager and a naturally headstrong personality, Anna refuses to listen to Elsa's age-appropriate wisdom. They become involved before Anna is 18 because Elsa, despite her best efforts, can't push her away and can't resist her either. There are lots of potential bad repercussions here and only one possible happy ending. (bad things: Anna grows up and realizes this isn't what she wants for the rest of her life, Anna acts immaturely and gets them exposed, etc)

option 7g - runs concurrently with all the above options - Elsa goes up the mountain to personally yell at Pabbie and/or Kristoff for corrupting Anna with their unconventional troll morality about "true love"