This is essentially the idea that we've been applying to seed funding firms with. The market for products for the elderly is huge, and software firms largely don't care about it. So, I think it is a great idea (haven't looked at your implementation yet).

I'll share with you one insight we had from our brainstorming sessions: we thought it would be a good idea to make the product a desktop email client that runs on startup rather than a web page (tagline: "Outlook for the elderly. Except it doesn't suck like Outlook."). I just remember how difficult it was for my father to learn how to find the browser, open the browser, go to gmail, remember his password, etc. And yet for many users, email is 90%+ of what they use their computer for. There's no reason it should be complicated (or use small fonts!).

However, making a website probably entails less up-front investment and allows you to test the market. It's a great idea, and I wish more people would focus on this underserved market.