He’s 10 months shy of being the oldest to accede to the throne.
He’s a long way though from being the oldest claimant - that would be the Electress Sophia, who at 84 died just a month shy of being Queen.
Charles hasn’t yet become the longest serving Prince of Wales. He needs another 4.5 years.
59 years 1 month (Edward VII)
57 years 5 months (George IV)
54 years 5 months (Charles).
Charles is also about 4 years away from serving as the longest serving heir presumptive. Only James Francis Edward Stuart served longer, 64 years.