The average age of light vehicles in operation rose to 12.1 years in 2020, according to research by IHS Markit. That is about two months older than it was in 2019, which was the previous record.
The reason for the increase, unsurprisingly, was COVID-19. The lockdown caused a decrease in new vehicle sales, which will tend to raise the average age. There was also an increase in the scrappage rate, according to IHS Markit, as working from home (or unemployment) caused some vehicle owners to let their registrations expire. The number of vehicles in operation (VIO) actually declined in 2020, down to 279 million vehicles. There had been 281 million VIO in 2019.
They also point out that the record new car sales years starting five years ago are causing a bulge of vehicles in the “aftermarket sweet spot” of vehicles that are between six and 11 years old, which should provide a tailwind to aftermarket sales growth.

IHS Markit also points out that the number of electric vehicles in operation is now close to one million units, with an average age of 3.9 years. As the number of electric vehicles increases, and more older EVs take up market share, there will be more opportunities for aftermarket repair.
See https://ihsmarkit.com/research-analysis/average-age-of-us-light-trucks-and-cars-approaches-12-years.html for more information.