When did you let your LO handle regular books without fear of pages being torn?

I know some parents let their kids flip through regular books early on without worrying whether pages get torn. However, our income is pretty limited and most of our books are from the library. I wouldn't want to have to replace their books when we can't even afford to spend that much on books for our own bookshelves.

I know accidents happen, but at what age were you pretty confident that regular books wouldn't be destroyed?