My assessment: it depends on the child. But two things have to be in play:
1) the kid understands the difference between right and wrong, and
2) the kid chooses to do the wrong thing
So depending on the kid’s maturity and and intelligence it can be anywhere from age 3 to age 5.
Example:
A 2 year old picks up a cup of water and turns it over and gets everything wet. That’s an innocent act of a kid who doesn’t know better.
A 5 year old picks up a cup of water, looks at mom, smiles, and purposely turns it over. That’s a wilful act.