I don't have any hard data, but I can say, anecdotally, most 50+ are not "techies" and they don't know their way around a computer system. I believe this belief is rather common.
I think some 50+ year olds would make exceptional startup founders. However, an older person who may be founding a "social, local, mobile" startup because he's looking for a career change is going to have a credibility gap because of the general impression that older people are not technically minded. If the pitcher doesn't have a strong compsci background or history to counteract that notion, he'll have to make up for it in the presentation.
We are all free to pontificate on whether this is a fair generalization or not, but I think it is clearly that it is commonly held and something an older founder will have to face and address if he wants to succeed.
