Do front brake pads wear out faster than rear?

My rear pads are low, but my front ones are probably 60% there. I bought all four sets with the intention of replacing all four and having them all wear out at the same time. I don't feel like replacing brake pads every 6 months. Do front brake pads wear out faster than the rear, and is it a bad idea to replace all four at once??? I drive a 2001 Subaru Outback