Gracious, not until MUCH older than 19 months. But I have to confess that one of the ways I got my toddlers to eat a decent amount of food was by encouraging them to just use their fingers. Neither of my kids are particularly inclined to small motor coordination, so using a knife effectively was something they did around kindergarten.
I think if your child shows an interest in cutting his/her own food and "practicing" using the grownup utensils, let them "practice" with a plastic knife on something soft, like scrambled eggs, green beans, or rolls.
But don't be surprised if the fascination with using a knife is a passing fancy that's more about imitating you than about seriously learning to cut food.