Add to it that E-5 avg is 4.8 years. The Cpl seems to have been on track.
Just looking at the timing of my USArmy (Infantry, Big Red 1) son-in-law.
He may be above average?
Recruit to E-5 in 4 years, squad commander in his 2nd deploy to Ghanny. Now a DI. Interestingly enough...he still has his squad command, too.
Made Cpl. in 16 months. Different time....