60 gal is borderline size for a Mandarin. If you want one you must avoid adding food competitors of Mandarin. Most of the wrasse that are used to control pest need to be avoid. Leopards also are not good tank mate of mandarin in small tanks. Fortunately fairy and flasher wrasse are fine. Small Angels should be avoid also.
you should have refugium and should have tank that are “pod friendly” substrates piles that are coarse with plenty of crooks and crannies that pods can live in and hid from predators. I have piles of small bivalve shells in the tank, on top of the sand. These piles provide perfect environment and protection for pods (until they venture out and be eaten by your Mandarin).
Using these rough guidelines I was able to keep a fat mandarin in a 28 gal cube for many years. This tank only have Crocea clam, small Magnifica, p pair of snowflakes clowns, a marine Beta and a male Mandarin.
I do not think how long a tank have been up have much bearing on it’s suitability for Mandarin, but how Pods friendly is of utmost important. Pods reproduce really fast so the pod population reach equilibrium quickly. No need to wait for years for this to happen.