For what it's worth, the plane as it crashed was barely an original aircraft at all. As with many warbirds its "restoration" arguably consisted more of dismantling the original aircraft, reverse-engineering it, and then building a new copy of the original from the ground up. Despite officially being a 1940s aircraft it was really only about 25 years old in practical terms, and in theory that should've made it pretty safe to fly.
We don't know why it crashed yet, but if it was the aircraft's fault it probably comes down more to core design issues than age. This is the second of the four N-9Ms to kill its pilot (the other two were scrapped before they got the chance), and its YB-35 and YB-49 also had serious handling issues, which in the latter plane lead to a fatal crash as well. Pure flying wings just don't seem to work very well without fly-by-wire and computer-assisted stability.