Perfect age to wipe?

So my 3 year old just expressed that he wants to wipe “all by himself” after he does #2. And I’m proud! Bc at this point, he stands and pees by himself and washes his hands by himself, and this would the last step of total independence during potty time. BUT I could’ve cringed when he said it 🥴😂🤦🏽‍♀️ because all I could think of is 💩 crumbs left in his crack & under his nails, stains in his underwear & him being itchy and smelly. I also know I can’t wipe his ass forever 🤷🏽‍♀️ So what age is a good age to start? How do I make sure he wipes efficiently? Is it trial & error 🤢?