Vasculitis is uncommon. Overall, in every 100,000 people in the UK, only 10–15 will develop vasculitis each year. However, about 22 people per 100,000 aged over 50 years will develop giant cell arteritis (GCA).The different types of vasculitis tend to affect different age groups, for example:
https://www.versusarthritis.org/about-arthritis/conditions/vasculitis/