If you go on google and look up feeding; you'll read that not only do you have to start at 4 months, but you should only feed them 10 tablespoons a day. Breast or formula milk should be enough substance and nutrients, correct? Well yes, they have all the nutrients a baby needs all the way to a year old, BUT some babies don't get full. You can always try to distract a baby, hold a baby, and try to pacify a baby, but when a baby's hungry: they're hungry. This is why some doctor's recommend putting rice in your baby's milk bottles. However, there's more then one way to determine a baby's readiness for solids. Age is just one of them. It's TYPICAL that babies around 4-7 months have the right qualifications to eat solids; however, all babies are different and develop differently. A baby needs to hold their head up good and should not have the tongue thrust reflex or "extrusion reflex."
Shiloh, my daughter, started to hold up her head good at 2 months and started drinking about 6 ounces every 2-3 hours. Milk just wasn't doing the trick anymore because she just seemed hungry all the time. Normally, a 2 month old takes 4-5 ounces every 3-4 hours. Obviously, Shiloh wanted something a little more. At first, I was very reluctant when my mom suggested feeding her solids. We started on the Gerber 1st foods and Shiloh took to it very well. It took a couple of weeks for the tongue thrust reflex to completely diminish, but she was a solid eating pro.
A lot of mom's will tell me that I'm a terrible mother and how it could cause food allergies down the road for feeding my baby early. Here's the thing, all I did was become attentive to my daughter and her actions. I tried the whole distracting and rocking my baby tricks; they didn't work. She was hungry and I'm going to feed her. Not only did I let my instinct kick in, I also did my research. Pediatricians want you to answer these questions before you start solids:
If you answer "yes" to all 3 of these questions, your baby is ready for solids. Some babies will be early such as 2 months and there will be late bloomers such as 6-7 month old babies.
The best way to determine rather your baby is ready for baby food other then breast or formula milk is trust your motherly instinct. You'll know your baby best.
References and good "What To Feed Your Baby" material: