Risks of getting ICL done at 20?

Hi everyone.

My sister is 20 years old and has extreme myopia ( around -18 in both eyes). She has suffered enough her entire life and has to wear extremely thick glasses every day.

She recently visited a doctor, and the doctor suggested ICL at some point. He did not rule out having the surgery at 20 but said patients usually are a bit older when they get ICL done.
My question is: what are the particular risks associated with ICL surgery at this age? If not now, when should she consider getting it? Her prescription has been mostly stable ( .5 increase) in the last 12 months.
I would greatly appreciate your suggestion and personal experience about it.