I agree with Ward, there's no reason why the manager wouldn't speak to you if you asked nicely?
My guess is you were probably angry and irate with whatever problem you were having and came across as an irritable customer. I find it hard to believe that they automatically treat you badly because you are young, as long as you are respectful, there's no reason why they should treat you any different than an older person. Case in point, when I first contemplated on purchasing the E90, I walked into the dealership with my buddy (we're both 27), looked around, behave in a respectful manner and asked for a test drive, the salesman did not hesitate for a second to hand me the key. From what I've heard in the past, salespeople are weary of buddies coming in for 'joy rides' and not being serious about buying. He commented on how he appreciated that we were very respectful young men.