Last night I literally woke myself up to write this down. Because it’s sort of awesome, if it’s a valid theory. Stay with me guys.
In The Time Traveler’s Pig, when Dipper tries to keep the timeline as the one where Wendy doesn’t go out with Robbie, there’s that part where Dipper tries to prove that Mabel will get over Waddles.
He uses the time machine in that timeline to go forward in time a whole month. For Dipper, that’s only seconds, but Mabel LIVED that timeline. Every second of it.
It’s obvious that it’s the same Mabel too, because she had to have remembered it in order for her to know that Dipper sacrificed his timeline for her to have Waddles again.
Which could be a perfect explanation for why Mabel grew a millimeter taller than Dipper instead of frequently being the same height as him their entire lives.
She’s not 5 minutes older than him now, she’s a MONTH older than him.
TIME TRAVEL LOGIC, WHABAM.
EDIT: Okay, a few people didn’t understand my reasoning, probably because theirs is better. But this is sort of the way I look at time travel.
If Mr. Spock (I needed an example name) goes forward in time from Point A to Point B, which is a span of, say, 20 years BACK, he is still a 2 year old (Let’s pretend that Spock is a time traveling baby okay?).
HOWEVER, if he lives in that place in time for 1 year without time traveling or anything, he would have aged 1 year, and would now be age 3.
SUDDENLY, IN A BRILLIANT EPIPHANY, Mr. Spock the time-traveling baby realizes how to get back to the future (heh), and takes himself 20 years into the future. He is STILL a 3 year old, even though he is at the same place he would have been if he hadn’t time traveled.
And Mr. Spock the time-traveling baby lives happily ever after, the end.
See? I know that gets more confusing when it comes to what Dipper and Mabel did, because they were dealing with, like, alternate timelines and stuff, but yeah basically my theory sort of still stands. Time-travel is confusing. Don’t play with time machines at home, kids.