OK so let's say it's ageism, why should I care again?
If your president can barely finish a coherent sentence and literally pisses in a plastic bag strapped to his leg I don't care how you call it but I want none of it
Same reason I don't leave my newborn baby alone with my 95 years old grandma who has dementia, call it ageism if you want, I call it basic common sense
It's usually used as a slur, though. Not letting 3 year olds drive is changing behavior based on age, but sometimes you should be treating people differently based on some external attribute they cannot help. If most people a certain age do not meet the minimum requirements for the task (such as being able to see over the steering wheel and having a good judgement about rapidly changing situations), it is not "ageism" to say they cannot do something. Banning 3 year olds from driving is different than only hiring under-40 software developers.
I bet plenty of managers/owners could make arguments about the over-40 group, like unwillingness to work stupid hours, whatever random tech stack they want, etc.