Baby wipes versus toilet tissue?

Howdy r/parenting, I'm new here. I have a question for you. At what age is it okay to use toilet tissue over baby wipes?

My son is a year and a half old and some change, and recently his mother and I had a conversation about wipes vs tissue. You see she and I don't make that much money, so I suggested maybe it's time to just use toilet tissue to wipe our son's bottom. Now, I may be mistaken, but I think it would be okay, and I don't think he'd get diaper rash any easier than he would otherwise. But his mother feels that wipes MUST be used or he will for sure get diaper rash and he will get it often. My son doesn't have sensitive skin, and I don't think he's even had diaper rash before.

Help?