Will chin lipo age my face? (Photo)

At your age, liposuction will not cause your skin to sag. You still have enough elasticity that it should conform quite nicely over the new contour. However, I’m not sure you have enough fat to undergo liposuction. I might recommend getting a second opinion with an experienced board-certified dermatologist for further assessment and treatment recommendations.

    From the limited  photographs presented, there does not appear to be enough fat in your neck therefore it does not seem worthwhile to undergo a liposuction procedure.  Even if you did have enough fat, the improvement is in the neck and will not age your face.  

The reason you have a slight double chin despite being young and the healthy weight is because your mandible is relatively small and lacks forward projection.
At the same time the shape of your chin is pointed creating an already slightly sharp labiomental angle.
If it wasn’t for the pointed chin then a chin implant or sliding genioplasty would be ideal.
The lack of projection of your chin often goes hand-in-hand with a slight dental overbite or an upper lip the projects further in the lower lip on a profile picture.
Overall your contour is fairly good and I think you’re a little over concerned about your chin beyond what anybody else sees as being an issue.
Of patients seeking chin fat reduction at least 90% have a mandible that is small or lacks projection.
Liposuction is remarkably good at correcting the problem even if it doesn’t address the primary  issue. A very simple way of assessing who will get great liposuction results it’s a gently pinch the skin in your chin.
Patients who can pinch half an inch or more will get impressive results.
Patients who pinch about 3/8 of an inch will see subtle improvements.
If the total thickness is a quarter-inch the Liposuction or any fat removal isn’t going to do much.
Obviously it depends on how firmly you squeeze and this is a pretty crude general statements.
Regardless, a small improvement in this area can make a very nice difference.
Most plastic surgeons do a decent job and it’s an area that isn’t messed up too often.
Probably nothing wrong with having the Liposuction done as long as you did your homework and picked a talented and experienced board-certified plastic surgeon.
Hopefully you had an in person consultation and were properly assessed before scheduling for surgery.
For patients who are at risk for a deepening labiomental angle from proper chin augmentation with implants conservative use of fillers can sometimes look good. 
It’s not uncommon for people to get cold feet or be apprehensive before having plastic surgery scheduled.
If the procedure is done correctly it will not negatively affect your skin. it simply doesn’t in young people.
I’ve been doing Liposuction for over 20 years in the last 10 years my career was focused only on liposuction and fat transfer procedures.
The whole notion of having a mandible that lacks projection but it’s pointed at the same time is a little tricky.
The perfect treatment would be to advance your mandible behind your molars.
That turns out to not be a procedure we know how to do without serious drawbacks.
Why don’t you contact your plastic surgeon and share your concerns and ask if you were she is willing to put it on hold for now.
You should also ask if you can come in to be seen in the next few days for a preop visit.
Expressed that you have concerns about moving forward with the surgery.
I would not be concerned about ending up with skin problems. Realistically there results will just be on the subtle side.
Seriously bad outcomes in someone like you rarely happen. Typically only if someone is using a high power device such as VASER inappropriately.
Have faith.
Best, 
Mats Hagstrom MD