60A @ 120V = 7200W
If there's nothing else running on that box at the same time, it's very feasible. Combine 2 elements to get to 5800W (80% load).
I use a 3500W induction plate (240V), and can easily boil 5 gallon batches (7 gallon wort). With the lid on half way and some insulation around the kettle, 10 gallon batches (13 gallon wort).
On older installations, make sure all the wiring is sound and sized correctly. There's a good possibility they used aluminum wire to your 60A subpanel, which may need some attention/checking.