AFAIK both Titan and Jaguar received significant mid-life upgrades. So in such a scenario 7 years sounds reasonable.
(At a previous job, we had a cluster that was about 15 years old. Of course, it had been expanded and upgraded over the years, so I'm not sure anything was left of the original. Maybe some racks and power cables.. :) )
ORNL's Titan lasted about 7 years: 2012 through 2019. Its predecessor, Jaguar, was 2005 to 2012. Also 7 years.