Peach tree is growing well but has not set fruit in 4 years; how do I encourage it to fruit?
It's not unusual for a fruit tree to take up to 5 years to reach bearing age, so it may just be a matter of patience, waiting for the tree to be mature enough to fruit well since it sounds as though the tree is growing well otherwise. One caution: you may be giving the tree too much fertilizer. High nitrogen amounts can stimulate lush vegetation at the expense of fruit. Try cutting back on the fertilizer.
It's also possible that late spring frosts could have damaged any flower buds in the past couple of years. Did you see any blooms on the tree?