Should I lose weight before seeking chin/neck liposuction? If I do this now, will it prevent it getting worse in the future?

Hello, in general I'd suggest trying to reach your goal weight before seeking chin lipo or other cosmetic surgery.  Not only might your problem improve somewhat, but the surgeon will be able to determine if there are other issues like loose skin.

Before any plastic surgery, it's probably best to be within about 10% of your target body weight.  The same would be true for liposuction of the neck. Most patients below age 40 have sufficiently good skin tone, such that suction of fat will cause the skin to tighten up.  Additionally since those fat cells are gone forever, the chance of gaining that fat back/problem worsening is less. In general, lipo of the chin tends to be a very effective surgery with minimal down time and limited complications.  Some patients may also require chin implant to get the optimal results. All the best!

 It is always best to be at your ideal body weight before undergoing elective cosmetic surgery including neck liposuction. For more information and many examples  please see the video and the link below

I would suggest losing at least half your intended target loss before making any decisions. Then you should see a facial plastic surgeon for an evaluation. At your age, there are some non-surgical options available as well as surgical options.