You will be assigned an ALO when you reach the Candidate stage, which is midway through your junior year if you fill out the Pre-Candidate Questionnaire early and are deemed competitive. You can fill out the Pre-Candidate Questionnaire after March 1 of your junior year, or alternatively, you can apply for Summer Seminar in either December or January of your junior year and designate that application as your Pre-Candidate application. In either case, you will be assigned an ALO when you are notified that you have become a "Candidate" and his/her name and contact information will appear on your application portal.
Having said all that, it may be the case that the ALO you are assigned is not the ALO who conducts your interview, which is some time during the Fall of your Senior year over Skype or Facetime. This year, we were temporarily assigned different ALOs until our interviews were done - then we were assigned a different ALO again. This is a new method that USAFA instituted this year and it might change next year if they think it needs improvement. Good luck!