Is 22-23 too young to be an e6?

I was up for E- 6 when I was 21, I didn't think I was to young, I had spent 18 mo. in Nam, but I didn't reenlist, so I wasn't promoted!!!

Too young to be likely, but E2 - E-4 get promotion waivers all the time, & Corporal or Acting Sargents, as well as battlefield promotions happen to.
We had a 1st Sgt in my HQ Battery in 83. He had battlefield promotions to Major during Vietnam. He was rifted on a few promotion lists & had to leave or enlist as a Sgt & worked his way up. You still Retire @ your highest rank served (Major).

In the Navy yes it would to young to unless your are Nuke on Subs or Carriers because they are E-5 once they are done with all the schools they have to do before they get to the first command. Other than that situation no. But, I have met a Chief (E-7) a at my last command on Guam back in 2009 he had only 7 years in the Navy, but he was Nuke on Subs, lets just say he had issues for a while.

I was offered a Commission but that would have made me just another butter bar

I would say not but this isn't the norm. At 22 - 23 most have not really reached full maturity (even if they think so). On the other end of the scale I have seen thirty-five year old E-6 and E-7's that were not very good leaders also. It depends on the person more than anything else.

Throughout Army history, there have been a number of highly effective leaders whose ranks and ages would be cause for a double-take at least in today's Army.

E-6 at 21 in Vietnam, I wasn’t the youngest in my unit

Yes. In my opinion you are too young. My last PSG was 24 and he wasn’t a good leader. He lacked experience and was very childish in his ways.