What age?

At what age did you introduce baby food to your infant? Our daughter will be 4 months in about 10 days. She's been really fussy at bedtime, screaming and crying which is out of the ordinary for her. My wife called her doctor today and they said we can start baby food and rice cereal in her bottle. We did so, to no avail. But, she did enjoy the bananas 🍌 
We originally wanted to wait until 6 months to start baby food but as long as we have the ok from her doctor, I guess we've started now.
How old were your LOs when you started?