You can measure telomerase activity with something called the TRAP assay. That is how they figured out that TA-65 works.
This interesting study may be the missing link to understand why stress ages us. It shows that the stress hormone, cortisol, decreases telomerase activity.
That is why learning to manage stress is healthy and becoming overwhelmed by it ages us. Look at JFK before presidency:
He had Addison’s disease so he required a lot of cortisol which made his face round. It probably kept his telomeres from regenerating like they needed too.