Can my 9 month old

Eat tuna?? And what age do you start referring to your baby as a toddler?

I don't see why not. And not until a year old.  

Yes its fine after 6 months old to eat fish. And at 1 yrs old

Toddler is 12 months technically although when my first started walking at 9 months in my mind she was a toddler. My youngest just turned 1 still isnt walking and she is still very much a baby/infant in my mind.

As for tuna i gave it to my daughter around that age with no issues.