Between the end of the Naruto and Sasuke fight (ep 479) and the beginning of Sasuke Shinden (ep 484), you can see that most of the characters have not only received a new set of clothes and hairstyle but have also aged quite a bit.
So how much time has passed?
Found this image on Light Novels page of Naruto Wikia. Light Novels - Naruto The page also lists the the timeline of the novels, but for some reason it doesn't list Sasuke Shinden. But there seems to be an official timeline, probably from Jump/Databook (Citation Needed)
I don't read Japanese, so maybe someone could corroborate, but looking at the covers, Sasuke Shinden seems to be in the same period as that of Gaara Hiden. Following this Sasuke Shinden take place somewhere between 2-10 years after Naruto and Sasuke fought in the Valley of the end
Edit: Correction. It seems the event take place just before Chapter 700 of the Manga, but after Naruto becomes Hokage so closer to 10 years rather than 3 that I assumed. However this is true only for the Light Novel and not the Anime. Found the translated timeline on Reddit: A guide to the Naruto Light Novels, Naruto Gaiden, and The Blank Period. It seems like the most complete timeline of Light Novels I could find.
In the Anime, Naruto is yet to be Hokage and there are several other discrepancies. No official timeline as of yet, but events seem to be just AFTER the events of The Last.
Edit: Confirmed for Anime too. The Events of Sasuke Shinden Episode 484-488 take place some time after the events of the movie: The Last.
Images for reference Below, Order (LtR- Official Timeline, Sasuke Shinden, Gaara Hiden):
From last battle, I think their ages were 17 years old. Probably Sasuke Shinden only takes 2 - 3 years after last battle, because when we saw the Naruto Movie Last, their face were look almost same with Sasuke Shinden, The Last Movie maybe occurred after Sasuke Shinden.
I've considered your answers, but I couldn't accept them, because they were either not supported by evidence or a bit vague (2-10 years, or closer to 10 years, is not helpful enough). Sorry for not replying sooner.
However, I did find the answer from anime episode 489. Here's a picture if you don't feel like watching it:
I know it's from the anime, but according to Animefillerlist, it's considered canon. So there you go, I answered my own question (very rarely does it happen!)
My first point, which is the most obvious, is that Naruto is 17 at the end of the fourth shinobi war. During episode 491 of the anime, while on a mission Shikamaru says "I'm only 19!" Presuming that Naruto and Shikamaru are the same age, this would mean Naruto is 19 as well; which would ultimately mean that between the end of the fourth shinobi war and the beginning of epsiode 484, 2 years has passed.
