I think it's less animosity and more incompetence.
I remember once when I was younger - around ~26 - being interviewed by a ~22 year-old fresh out of college, and the interview was more like a college test.
What relevance did this have to what I would do at the company? Most likely - nothing.
But this was basically all this person knew.
The younger you are, the less ability you have to 1) know what's valuable, and 2) assess it.
Not that this is a particularly easy thing for anyone to do.
That being said - younger people are going to place close to no value on your decades of battle scars and experience. They don't have any. They probably like to think it's not worth anything - because it makes them feel better about not having it.
You know - never attribute to malice that which is adequately explained by incompetence.
I'd also caution on the things you perceive to actually be animosity - they're probably mostly jealousy. You're someone who has WAY more options available - so you can be demanding and picky about your employer. Younger people might hate that - but that's really jealousy. They probably don't actually hate you. There's a big difference.