The Elephant's Trunk Nebula lies to the right of the bright central star in today's APOD.
It's interesting to look at this fine picture to try to judge, from pure visual appearance, the (relative) age of this nebula and its central powerhouse. IC 1396 is a typical emission nebula ionized by one or more hot stars of spectral class O or very early B.
All O stars are young, but they, too, go through phases of their evolution. Often you can make some sort of guess as to the age of the O stars based on the surrounding nebulosity (or lack of it).
IC 1396 is a large and comparatively faint nebula. The central star, HD 206267, is multiple. My software identifies at least three companion stars orbiting close to HD 206267, which may itself consist of at least two components.
Apart from the tight grouping of hot stars at the center of IC 1396, there is only a scattering of hot stars, quite widely separated from each other, inside the nebula.
The nebula itself looks relatively "smooth" near the center, although there are many dusty structures in the outer parts of it. The center has not been "blown out", and there is no "cavity" in the center. There is one obvious site of ongoing star formation in the larger nebula, which is, of course, the small part of the nebula called the Elephant's Trunk.
We may compare IC 1396 with the Lambda Orionis Nebula
. Like IC 1396, the Lambda Orionis Nebula is a huge, faint structure with a tight grouping of hot stars in the center. However, unlike IC 1396, the Lambda Orionis Nebula is almost completely smooth, with no obvious dusty structures at all, and no sign of ongoing star formation. We may therefore infer that the Lambda Orionis Nebula is older than IC 1396, because the nebula is more "dispersed", and all star formation has ceased.
We can also compare IC 1396 with the Rosette Nebula. Unlike IC 1396, the Rosette Nebula has a very obvious cluster of hot stars at the center. Unlike IC 1396, the center of the Rosette Nebula has been "blown out", so that there is a cavity in the center. The outer parts of the Rosette contains many dusty structures, but there is no obvious star formation going on, and the Elephant's Trunk Nebula in IC 1396 has no obvious counterpart in the Rosette Nebula. We may therefore infer that the Rosette Nebula is older than IC 1396.
Another Nebula that warrants comparison is NGC 2264
, powered by the central star S Monocerotis (S Mon). This nebula is not round, and its interior is turbulent. S Mon has blown out a small cavity around itself, but there is a lot of nebulosity close to it. There is not really a concentrated compact cluster in the nebula, but several young and relatively bright stars are scattered there. Obvious star formation is going on in the Cone Nebula. Because of the irregular appearance and all the central activity in this nebula, we may infer that it is younger than IC 1396.
It should be noted, too, that both S Mon and HD 206267 are somewhat faint as O stars go. This suggests that they are "unevolved" and therefore young. Both Meissa and the central stars of the Rosette nebula are intrinsically brighter, suggesting that they have grown brighter with age, as stars tend to do.