Probing can be done at any age.
When probing you have be sure that you are using the right sized probe, you are using a water based lubricant, that the tail section is held firmly as well as straight at all times and that not too much pressure is being applied once the probe has entered the animal.
It is good that you are going to have an experienced person do this for you as it it possible to injure your snake if this is done incorrectly. Have them work with you to show you how the probing process is done!