I made Mom an apron for Christmas too. This one is made from 2 of Dad's old shirts and is reversible. A couple of years ago, I saw an apron in Macy's that inspired the tie part for this project. There are just simple loops on the sides that the straps go through before they tie at the waist. The pictures will make it more clear.
Backside with normal tie (sorry for the off-center, poorly tied bow)