What the nature of the desired tooth movement is has more to do with
whether Invisalign is appropriate than age (except for children)

Steve (was 50 year old Invisalign patient)

do you mean that she needs four teeth out and then Invisalign?

unless the clinician is very, very experienced and the patient is
willing to live with less than a perfect result (call it a B result
when A is perfect), this does not sound like an Invisalign case.  If
the patient has any significant perio disease, forget it completely.
charlie ruff
orthodontist