Hello Loretta Harting,
You can start any time. Purchase your materials, study, take the test. Just be sure to finish within the specific time frame. This takes commitment; so, be absolutely sure this is what you want. You may do better to take a personal trainer education course at a college, first.
Natalie aka NAPS 2 B Fit.
Here is a link for you to contact ACE directly to start your certification proces.
Good luck to you!