Can i use a 60w led instead of a 60w incandescent bulb in an outside post lamp?

You could but it would be extremely bright! An incandescent lamp of 60 watt is about 800 lumens And so a 10 watt LED lamp should be plenty big enough. If you want as much light as possible instead of energy saving then you can fit bigger wattage LED lamps. Also, because they run a lot cooler, you can often exceed the maximum (Incandescent) rating for the fitting.