There has to be someone who should be age X physically but is actually X-1 years because of time dilation. They may have been born on Earth and also be back on it and alive for the claim to be YES. Also they have to not have died before returning.
If there is cryonics or eternal youth or something like that, evaluate based on the spirit of the claim. Someone who, if they had been conscious and normal and survived, would have seen a clock they were with cover at least one year less. Teleportation or other similar issues can't qualify or disqualify.
With some approximate math considering only special relativity, this is a bet that humanity will be able to devise a machine that can accelerate indefinitely at 0.2 m/s^2 within the next year. The machine would achieve peak speed of ~0.80c in 2062, before immediately beginning deceleration at the same rate. Waiting longer to build it means higher acceleration requirements.