What is the average upper hearing limit for adults?

Young adults with healthy ears hear up to about 20 kHz, but the upper limit falls with age. Studies of extended high-frequency hearing find most people in their 30s and 40s top out around 15 to 17 kHz, and by the 50s many cannot hear above 12 to 14 kHz. The loss starts at the highest frequencies and creeps downward as hair cells at the base of the cochlea wear out.

Source: Rodríguez Valiente et al. (2014), International Journal of Audiology; ISO 7029:2017