More important than number and age is operators and cause, into which age may matter or not. Will a newly off the line plane have the same problems from maintainers that one that is a few years over the expected lifespan? The above chart is nothing more than useless to make any comparison that is important.
One bit that is noticeable is that there was a sharp increase in incidents for Boeing when Airbus incidents increased. I'd look to see if that latter part was due to a ramp up in Airbus sales, causing some Boeing planes to be transferred to secondary operators with less capable maintainers or more short-haul flights that ramp up minor damages or simply getting to the part of their life where problems accumulate and the best maintainers were put to concentrate on the new Airbus purchases.
Let me look at the chart to see if that conjecture is true - and there it is - nothing.