Some claim domain age ain't that big a factor but for me, I would think that it is. If I were Google, I'd say that time filters out the quality sites - coz if it ain't quality, it probably won't last long in the web right? It's a good filter and I think Google's using it even if it's not a colossal factor, it still is - and in SEO, all factors are studied.
If you register your domain for 2-4 years, it would be better than just 1-2 years. Google knows. We can't really say what works or how much effect something has on your page rank. But if you know it might have an effect, why not go the extra mile? After all, SEO is all about going the long road.