Is it unsafe for a 18 year old be able to get facial liposuction?

Lipo at 18? It is not necessarily unsafe to get facial liposuction at 18, but it may very well be unwise. In general, it is not a good idea to remove facial fat in most cases. A bit of contouring of the facial tissues through open or closed liposuction may be useful at times, but I wouldn't suggest this procedure to an 18 yr. Old.
Yes. Facial liposuction is a very bad idea. Facial fat is precious and is very hard to correct deformities, irregularities and skin adhesions caused by facial liposuction.
Safe but... Liposuction of the face is not an “unsafe” procedure but is not indicated for the vast majority of patients, regardless of age. Generally speaking, fat in the face tends to be “youthful” looking; generally removal of fatty tissue is not wise.
No. Not unless you have an underlying medical condition that would prevent you from having anesthesia or any type of surgical intervention.