I think it just depends on when you're ready! After all, a baby/toddler isn't really too conscious of how they look! We waited around 2 years for my daughter's first haircut, but my parents gave me a haircut when I was probably around 18 months. I think it's really a matter of preference!
It's a family tradition (my side) to have the first haircut once the baby reached 1 year old. And before you bring the kid to a salon, a smart/intelligent family member must cut few strands of hair first because the elders believe (pamahiin) it will make the baby smart as well.
In our family, we usually have the baby's haircut when he/she reaches 1 year old. I don't know but it's been a family tradition not to cut the hair earlier than 12 months of life. And it's the usual practice to have the new haircut in time for the first birthday party. :)
The kids in our family had their first between 12-18months old, as it depends on the length of the hair of the kid.