Tom Cruise looks exactly the same today as he did when the first film came out, so they could set it whenever they want.
I mean, seriously, they could have it start the day he returned to his own unit after graduating and nobody would say "Wait a minute, how come he's like 30 years older now??"
That said, it would be interesting to see which direction they go. When the first film came out the F-14 had been in service for what, just over 10 years? While a decent amount of time, back then I feel not a ton of people had access to see/know about fighter planes so to them it was new and cool. Today though? Even though the Super Hornet would probably be the plane most likely used, most people would just see it as a Hornet, a plane that's been in service for over 30 years...and while I'm not trying to say Hornets/Super Hornets aren't awesome machines, they certainly don't carry a "Wow factor" like the F35 and its variants...so I feel the film would almost have to feature something that has a "Wow factor."
The problem with these planes (other than their real-world problems) is that literally everything I've seen and read says that they are basically unfair. A few years back I watched a documentary on the F-22 where a pilot being interviewed said it's not a fair fight until it's like 11 on 1. I've also seen a documentary where it showed five Raptor pilots in F15s dogfighting one Raptor...and none of the guys in the Eagles even SAW the Raptor before they had been "shot down." I remember one of the pilots saying "You only know you're in a fight with an F22 when you're below a parachute watching your plane fall to earth below you" or something to that effect.
Now is some of that hype and a bit of propaganda? I'm sure it is...but there's probably a bit of truth to it as well. While these pilots are still trained for up close dog fights, that is a last resort. Why get in close and dogfight when you can kill your enemy before he even has any clue you're there?
What I'm rambling on about is that nobody wants to watch a movie where a plane goes up, tracks 18 different targets at once, fires 8 missles, kills those targets, then goes and lands. While realistically that's incredibly impressive...from an entertainment standpoint it sucks.
So yeah...it would be very interesting to see what direction they tried to go.