What age do babies start to sit up?

well it actually depends when your baby is ready to be sitting up if its not sitting up at usual time that you think do worry about it. It really is normal but if you think it isn't then see a doctor

http://www.babycenter.com/0_developmental-milestones-sitting_6505.bc

the average age for babysitting is 13

Even though many of the "experts" say to start babies on baby food at around six months old, I started mine on a little cereal mixed in with their formula when they were six weeks old. I started out...

Some babies sit up by 6 months. Apparently, however, not sitting up by 9 months isn't a big deal either. See the Related Link to a video regarding a baby's milestones - sitting included.