I think not much, maybe Cade has long hair, because he is in some sort of depression after his daughter went to college and forgot about cutting hair, they may grew back for a year
Cade handled the death of his wife, crippling debt, and the death of his friend well enough...I'm sure he can handle his daughter going to college without sinking into a depression, lol. I would like to see him regress a bit and start cooking everything with ketchup again, though! Anyway, I'd guess it's the standard 3-5 years between films.
I don't think depression can be defined by hair length! And remember Cade doesn't age like other people. High School Cade looked just like 40+ year old cade in a cap!
Before the movies followed roughly the time in the real world between films. Which kind of worked since it could fit in with the ageing of the star. With this movie I don't think the main actor getting older will really be an issue but it seems like matching up to actual time between films so I'm not sure why they would change something that was working.
The 5 year gap between DoTM and AoE seems like a semi plausible time frame for Chicago to be rebuilt. It saves them from having to show a devastated Chicago for any extended amount of time.
Y'know what? I just remembered that there's supposed to be a montage of Transformers living on Earth in this film. Plus, there's the whole space-time thing we gotta think about, with Optimus traveling to wherever-the-hell and back. True, this is a sci-fi movie that doesn't give a crap about being totally accurate, but still. What if TEN YEARS (at the least) have passed?
Technically, Transformers: Dark of the Moon and Transformers: Age of Extinction both took place IN THE FUTURE relative to their release dates. So Transformers: The Last Knight would have to shave a few years off to synch back up with our real life timeline.