Unless I am mistaken, your average needs to be 61 or below to be eligible to be promoted to Legend.
This is certainly one way to get to Legend... if you play a lot of ranked rounds.
For TMs, the saturation number + minimum ranked rounds to Legend is only 50. Often, 61.00 avg. is much harder to achieve.
+10 to the following thoughts.
@H: Also, you may be stuck between promotion paths if he has more than a few RRs before switching to "mobile" games.
Eventually, you will be promoted when the games allows for it, so stay happy and have fun!