I started solids around 5 months. My ds was interested in food and loved watching us eat and was happy to have the spoon with food in his mouth - didn't push it out with his tongue.
As for timing of solids - you offer it AFTER milk, not before. Milk (as others have said) is the important part of the baby's diet and solids compliment it. So you offer milk first and solids afterwards.
My ds wasn't on 3 solids meals a day til 7.5 months and even then that only lasted a few days, before he went back to twice a day. He was a bit all over the place (and so was I with trying to fit in the solids meals) with meals til maybe 11 months of age ... but he kept up with 4 - 6 (sometimes more) breast feeds a day and grew well .