Telomere repeat amplification protocol (TRAP) assay works well. However, some optimization may be needed to detect the activity in normal cells. See details in our paper in link below.
ScienCell recently developed a qPCR-based, non-radioactive kit for measuring telomerase activity. The entire procedure can be done in one day, with hands-on time less than 2 hours. The primers' qPCR efficiency is close to 100%, making accurate quantification of telomerase activity possible. For more information, please go to:
https://www.sciencellonline.com/PS/8928.pdf
ScienCell also offered a few telomere length quantification by qPCR kits for human, mouse and rat.