Getting my snake sexed?

How old/long does my snake have to be to get her sexed by a vet?
I don't know how old she is, but she's about 20 inches long, and very healthy.

It can be done at any age.

Any age any size. Vets like to probe and IMO they sometimes dont know how to properly do it without causing problems from going too deep.

Thank you. :)

I pop sex upon babies hatching and fully coming out of the eggs I agree I've seen bad bad things happen with bad probes. It can permenently damage snakes. Popping is the way I'm comfortable with. I've never even learned how to probe.