Hi S.,
Our ped. had us start our daughter on cereal at 4.5 months. We gradually worked our way to stage 2. She's now 7 months and I think we started her on stage 2 at 6 months. We are now using the last of stage 2 and starting stage 3. I've found the stages thicken just a little. I also starting giving her biter biscuits (messy) this week. Once your baby gets used to it, try the Gerber Graduates Puffs. They look like little flowers and I crack off two (petals) and give my daughter the rest. They melt in her mouth. I started today giving teeny tiny pasta stars.
You probably already know, but breastmilk/formula is still the main source of food & nutrients.
Like the others, every baby is different and you can tell when your baby is ready to explore. It's funny to watch their faces when giving the different textures. Get your camera ready.