I've seen several times that some pediatrician's recommend starting solids earlier (at about 4 months) to avert allergies. My own pediatrician said to wait until 6 months to avert allergies.
While I trust DS's doctor, I also would like to do research myself (not just about when to start solids, but other things as well, for example, when to start potty training). How do you research these things? The internet is not reliable, nor is any one person's (the doctor's) word.
Also, how long has your pediatrician been in practice? Maybe that's why mine recommended 6 months; he's been a doctor for at least 20 years. Are the "newer" ones more knowledgeable, or does it really matter?