There are different schools of thought over deleting old content. One is that, as Google will only crawl so many pages on your site each day, there is merit in deleting really old content because it focuses the crawl budget. However, my view is that whilst this may make sense if you are posting 50 articles per day, it really doesn't apply if you are posting 2-3. Personally I would be more concerned over the impact of having lots of broken links into my site from people who have quoted our old content. I also think there is merit in having old content to the extent that Google puts value on site longevity and because people DO still search for terms no longer used, like SPG points.