Does tube testers tell how much life is left for tubes?

A calibrated TV-7 was good at that, checking life and shorted tubes, i have used one for some time, could not match tubes though. If going into tube testers and want matched tubes better invest on a modern one that can measure in actual conditions, or close, transconductance, plate current, leakage and mu.
Otherwise use your tubes close to the safe end of their lives.
Tubes are not created equally so you cannot tell from heater element glow if they are good or bad.
Actually you cannot tell if they even work.
You could monitor though a specific tube for changes in glow with usage.

Thanks for the info (even to MC).
I have two tube testers. One from Knight and one from Superior Instrument. Both is I guess made in late 50s or early 60s. They don’t have transconductance readings. They tell whether tubes are good or bad, but they don’t tell how much life is left.
If in doubt, I would just purchase new tubes to be safe.
The new (old) preamp I just bought (A.I. M3B) is recommended to have tubes replaced every two years. Yikes!

short answer is even the best tube testers measure the present degree of mutual transconductance of a test subject tube - it is a decent proxy for tube strength/freshness but it is a poor proxy for durability as a function of time

if you want to educate yourself more...

http://www.alltubetesters.com/articles/tester_guide.htm

http://www.jacmusic.com/Tube-testers/

https://shop.ehx.com/vacuum-tube-faq/ - see section on tube testing

I use the uTracer and i am happy with it. Most important for me is transconductance.Only in German, sorryhttps://www.orangeaudio.de/blog/2021/04/29/roehrenmessung-mit-dem-utracer/

An approximation of tube life can be found from the cathode emissions, which I think some testers can provide.

When the cathode electron emission drops way low the tube is at the end of its life.

Tubes can test good right up to the end time of failure.