Hi Prof. Nelson,
I noticed that the stellarage property is available when plotting using the web-based API, but not available in any other catalogs that I can download and analyze locally. I wonder if that's true so that I have to calculate the mass-weighted stellar mass by myself based on the snapshot.
Yes it's true this field is running a small computation, since the value is not directly available in the group catalogs.
If you want a particular simulation/snapshot I can send you a link, otherwise it is a fairly simple computation (mass-weighted, or light-weighted, average stellar age of star particles of each subhalo, as you describe).
It would be very helpful to have the catalogs for TNG100-1 at snapnum=099, snapnum=067, and snapnum=050. Many thanks!
You can find these files (temporarily) here