I completely missed this thread. I'll give my take on things. I grew up with my Grandparents. I ALWAYS was around adults. My Great Uncles and Aunts, Grandparents church friends, etc. I always listened to them and as I got older I got brought into conversations. Never once was an opinion of mine discounted simply because I had less birthdays.
Everyone ages differently, experiences life differently, and views the world differently. Growing older is simply part of life. It doesn't make you smart or special. When you debate someone and use age as your crutch it just shows your true lack of ability to reason and debate.
In my opinion, telling someone they don't know because they are young, is the same as telling an elder they don't know because they are old and out of touch. Neither is very polite.