This will vary home to home, but I recommend introducing scissors between 2-3 years old. Kids then can become comfortable with scissors between 3-5 which support their use in school.
First off, I’m left-handed and so is my husband.
Lefties are incredible. There are many things we have to adjust while living in a very right-handed world, although it is often boiled down to just scissors. It’s more than just scissors.
I use right-handed scissors in my right hand. That’s how I adapted. I’m very grateful I learned on right-handed scissors because the world doesn’t have left handed scissors. In classrooms, offices, friend’s houses, businesses, and every junk drawer: right handed scissor are what’s available.
If I used left handed scissors, I would need to carry scissors with me always OR not be able to participate in cutting anything outside my home. I’m so glad I can use right handed scissors. It makes my life more accessible for me.
If you have a child who is left handed, I suggest starting with right handed scissors. Many lefties use right scissors in their left hand. That’s their adaptation. They can still use scissors out in the world, they just move them to their left hand.
Your child also might do what many lefties do: right handed scissors in our right hand. Don’t be shocked by this.
If your child is struggling to find an adaptation, then I would buy a left handed pair of scissors to see if that helps. Some lefties don’t adapt on this. That’s ok! I never adapted to using an ice cream/cookie scoop in my right hand (yes, that’s another thing we have to adapt).
Lefties are amazing. You can best support your leftie by giving them freedom of choice. Do not force them to use their right hand and do not assume they’ll always use their left.