How old are military c-17 first officers wen they start flying?

First, we are not an airline. They are co-pilots, not first officers.

The bulk of USAF pilots come from USAFA and AFROTC. Most USAFA graduates came in straight from high school, so they are about 22-23 when commissioned, and therefore around 23-25 when they finish UPT and show up at their first base. Most AFROTC grads are of a similar age, and OTS grads are generally a couple of years older.

If you haven't started to look at USAFA or at least AFROTC, then you should start now.

Your best shot at a pilot slot is USAFA, followed by AFROTC as a distant second. If you are putting your hopes in OTS, you will probably be left in the cold.

Also, you only get a seat in pilot training out of your commissioning source (no guarantee of any specific plane). In order to get C-17s, you would have to get T-1s after T-6s (probably not hard since a lot of people will want T-38s), and then do well enough to pick C-17s after T-1s (versus tankers or any other transport).

you will be 21/22 by the time you get your commission and flight school runs toughly 2 years. so 23-24 on average.

Flight school is after college, and takes a year or more. So around 23 or 24.