Longer than most Enterprises before it.
Is it?
The NX-01 went 10 years, and by all accounts was probably decommissioned due to advancing technology, mixed with the fact the ship took one hell of a beating over those 10 years.
The 1701 had a good run at 40 years.
The 1701-A went 7 years, but we don't really know what was going on with that. Was Kirk given an aging ship that was renamed? Was she a total new build that just just became quickly obsolete? Was she crippled at Khitomer by the Bird of Prey?
The 1701-B? We have no real idea. We don't know when the C was launched. The B could have had an over 40 year lifespan.
The 1701-C? Same as the B. We don't know when it launched.
The 1701-D had a rather short 8 year lifespan.
The 1701-E had a lifespan of no longer than 14 years, if background info on the F is to be believed.
But it could have had a good 29 year run, if we didn't shoehorn in the F.
The NX-01, the A and the D certainly bring the average lifespans down. But at least those have some extenuating circumstances behind them. Bringing out the F, just for it to be decommissioned early is still a sore spot for me. Especially when we could have had a decently long-lived Enterprise-E.