In the Corps, avg to Cpl is 26 months. Don’t know how long he was one, he could easily be above average. If he was working for crewchief, he would be ahead of the game. 53E is a complicated machine. Perosnally I hate it although when it works, there is nothing like it but more guys I knew have been morted in that airframe than all the rest of the Corps inventory combined.
Add to it that E-5 avg is 4.8 years. The Cpl seems to have been on track.