I have a similar desire but across all search results, so my default search engine is a custom one: Google (Within Last Year). This has the same effect as when you click 'Tools' and select a date restriction, but automatically applies it to default searches.

You can add this to Chrome by going to Settings -> Manage search engines -> Add. Name it 'Google (Within Last Year)' and make the Query URL 'http://www.google.com/search?q=%s&tbs=qdr:y&tbo=1'. Then set it as the default.

This filters out of date and usually irrelevant search results across the web. You can override it manually from the 'Past year' dropdown if the results are not extensive enough, which I do maybe 5% of the time.

I wouldn't necessarily be against this but it would have to be filtered for certain technologies and even then it gets messy. Perhaps some internal SEO management, or newer relevant thread linking system would be better. Some technologies I use are OLD and haven't changed in the last ten years. Sometimes a 7 year old post has exactly what I needed. If they could add a banner and lock down voting and commenting after 3 years, that would be acceptable.

While that would benefit StackOverflow, it would cause a lot of issues when searching anything remotely obscure. I've ran into many questions that haven't seen activity since 2012 and don't have any newer ones.

It still confuses the hell out of me. I feel like every freaking question about swift I searched are always 5 to 7 years old.