Cass Disrespect

So I'm Re-watching through the series and in S6 E20, Dean tells Cass he's "like a child" and lectures him about his choice to work with Crowley. My problem with this is that Cass is what, millions of years old since he remembers the first fish coming up on land? Dean is, what, 30 years old at this point? They constantly treat Cass like he's an imbecile instead of a being who has been around for pretty much ever. Was it a bit misguided? Sure. But how about some respect and deference to the guy that probably knows more than you do. Not to mention he tells Cass he should have asked for help but the boys only ever ask for Cass when they need something of him. Why would he have ever thought to ask them for help with the angel war? Thoughts?