To suggest that the crash was a result of his age simply because of his age alone is ridiculous.
Whilst I typically
hate speculation, I think there's some evidence in the photographs - which along with previous accidents might give an insight into what happened. These are photographs of the aircraft;
Notice the lack of an elevator trim tab in the first photo. There was a previous incident a few years ago when during fast level flight, the trim tab of another P-51 (Voodoo Chile) broke off and the aircraft pulled into a 10G pitch-up. The pilot at the time was Bob Hannah. He immediately lost conciousness, and woke up having gained almost 9000 feet. If you look at the photographs of his aircraft 'Voodoo Chile' after the incident, you'll notice it's the same trim tab that went missing.
Also notice in the second photograph that you cannot see a pilot in the cockpit. One way or another he must be slumped forward, very consistent with heavy positive G.
And let's face it, I doubt there's anyone in the world who can stay concious with a completely unexpected and immediate 10G load.
Furthermore, the testimony of people on the scene suggests structural failure.