Wiktionary
gerontophobia
n. 1 abnormal and persistent fear of aging or growing old; gerascophobia 2 abnormal and persistent fear of elderly individuals or people 3 aversion or hatred towards elderly people
Wikipedia
Gerontophobia
Gerontophobia is the fear of growing old, or a hatred or fear of the elderly. Many people have this phobia. The term comes from the Greek γέρων - gerōn, "old man" and φόβος - phobos, "fear".