At what age is it best to start getting Ulthera and Thermage?

I have chubby cheeks, so I am considering Ulthera, Thermage, or InMode.

I thought it wouldn't be good to receive it when too young. At what age is it generally recommended to start receiving it?

What do you think is a reasonable amount?

I previously had a consultation at a famous dermatology clinic in Apgujeong, and they quoted me 300 for Ultherapy.

I don't know if I should consider the price reasonable since it's a good place, or if I'm getting ripped off.