The US Navy retired the F-14 in 2006. The only military in the world still flying the bird is Iran, due to their appropriation during the 1979 Islamic Revolution. The mountainous environment seen earlier in the trailer could very easily be in the vicinity of that country or a Qurac-like analog. It would allow Maverick to return to the Indian Ocean setting of the first film, as well as "avenge" the "dishonor" of the F-14's "theft". It could even setup a showdown between Mav and the semi-mythical Qaher-313, a plane, real or not, that seems tailor-made to serve as a cinematic antagonist craft.
Easy. He put the brakes on his career and let everyone else fly right past him.
How did he remain a Captain for a long time? A naval aviator who reaches the rank of Captain is typically offered two possible command billets. He could have been a CAG (carrier air wing commander) or skipper of a nuclear powered aircraft carrier. Usually, it takes about 22 years to make Captain, after which a CAG command or carrier captaincy lasts for three years. It is possible but very rare for a CAG to take a lateral promotion to carrier skipper, but before doing that, he has to complete a deep draft command ie command a large ship such as an oiler or cargo transport which familiarized him with how to manage a large carrier. So, a CAG command, deep draft command and carrier command would have pushed it to nine years as a Captain. With him returning to TOPGUN, that would have pushed it further, but this is most likely his swan song tour.
If he hasn't been shown in person in any of the trailers by now, chances are he's going to be the one in the casket.
The film's synopsis states that Maverick is drawn into a confrontation with his own deepest fears, culminating in a mission that demands the ultimate sacrifice from those who will be chosen to fly it. Given this, and the emphasis in the trailer on Maverick 'refusing to die', the ultimate sacrifice could mean Maverick's death — making the funeral in the trailer a Bait and Switch since lots of people think it's for Val Kilmer's character, Iceman.