We shouldn't wait until after a piece of infrastructure collapses to fix the cracks in the foundation. The public capital stock has been allowed to age much more than the residential and private stock:
Measuring age is not necessarily relevant - if a bridge has a lifetime of 50 years, but the average age is 23 years (up from 16), we have a long way to go before it becomes a problem. Your chart is interesting, but hardly conclusive.