Tokyo Drift is the biggest offender, for obvious reasons: Lucas Black (Sean) was 22, Zachary Ty Brian (Clay) was 23, Nikki Griffin (Clay's girlfriend Cindy) was 28, Nathalie Kelley (Neela) was 21, Bow Wow (Twinkie) was 19, Leonardo Nam (Takeshi's friend Morimoto) was 25, and Brian Tee (Takeshi) was the worst at 29. Only Bow Wow was still technically a teenager out of the cast.
Both Toretto (Vin Diesel) and Vince (Matt Schulze) were said to be 24 when The Fast and The Furious has been made. Vin Diesel was 34, Matt Schulze was 29 by then.
Well, Schulze was still in his twenties at least. Diesel, however, passed pretty well for 24-year old Toretto. (Many have jokingly attributed Diesel's younger appearance compared to his real age to his love for D&D.) However, the actors for Tokyo Drift easily stand out as people older than their character's ages, Dawson Casting at it's damn-near worst.
Sung Kang was 39, 36 and 34 respectively when filming Fast Five, Fast and Furious and Tokyo Drift. Granted, we wouldn't be able to pinpoint Han's actual age in the films, but it's freaking amazing how Kang manages to pull off the role looking young.
The fifth film actually started out as The Brazilian Job, the proposed sequel to The Italian Job, when the sequel went through Development Hell, the script was bought and rewrote to fit into the FAF series.
Certain versions of the DVD, as well as Blu-Ray copies of the original have what was going to be an alternate ending; Brian is dropped off at the Toretto home, now for sale, to find Mia packing up the garage. Mia tells him to go, before Brian reveals he quit his job as a cop and was hoping for one more chance, before cutting to a wide shot of LA. Given how the following sequel paints Brian as running away to Miami for a new start, it would have been interesting to see the current films if the alternate ending was used.