Wormholes, possibly.

Isn't a wormhole a gravity well?

Grow older. At my current age it seems five minutes passes in a minute.

I hear that, but I mean more than perception but measurable differences.

Sounds like something you should be asking physicists.

You don't need to approach lightspeed. Any velocity through space is at the expense of your velocity through time, which is what time dilation is. It's just that it's pretty negligible until you get to a decent fraction of lightspeed.

Any curvature of spacetime will do it. A wormhole is a valid example. There's always been talks of warp speed engines that contract the space in front of you and expand the space behind you.

Wormholes are theoretical.

I'm not sure how much gravity they are supposed to have but it's the tunnelling through spacetime that could make time travel possible. In SG1 solar flares caused them to travel through time when using the wormhole in their stargate.

Yes and No, it doesn't require the extremes you mentioned, but it does involve the variables. The GPS is adjusted for both. One for the distance to earth's gravity as well as the speed of the satellites. I think there is an implication of an ambient time. The shape and volume of space in the absence of mass and the effect on an object without any kinetic energy. Whatever that would be.

Acceleration and gravity are essentially equivalent and both affect time "dilation". GPS (satellites located in a lower gravity position relative to the surface of the earth) and atomic clocks flown at altitude both exhibit the predicted changes in time (rate of change).

The twin paradox - if that is what you mean - is part of Special Relativity, no need for acceleration/gravity.