Lots of mom's have given baby food at 4 months. I personally skipped cereal and oatmeal though.

I started my DD on solids at 5 1/2 months. It was recommended by her pediatrician. She was under 6lbs at birth and to this day is still a little under weight. She's 3 1/2 and weights about 30-31 lbs 38in tall. She was formula fed but started actually loosing weight being just on formula. So to help her gain weight she was started on solids a little early. Typically 6 months is a good age to start or when they start showing interest in food past the age of 6 months.

I'm just wondering if any momma has feed there baby at 4 months she told me oatmeal

4 months is the earliest babies can have food. 6 months is the recommendation. Even at that age "food before 1 is just for fun". Do what you feel is best for your child.