A new recruit's level is determined when you look at their enlistment papers. Take the average level of your recruits, rounded down, then subtract 1.

Quote Originally Posted by Dorjee View Post
shouldn't I just wait until I level my current core squad of four to 60, before working on a new squad of four?
Not all the way to 60, but get them to around 40 with just the initial 4. You can blow through the low levels with just 4, do three daily training runs then the 18 hour mission. A failed mission still gives half exp, so don't worry about not having a 100% success rate.