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.
You said Charles is 54. He was born in 1948, which makes him 64.