I also started DS at 5.5 months, after about a month of him screaming the place down every time I ate something, even if he had just had his milk. I fully intended to wait to the full 6 months but in the end I couldn't bare the screaming any more and I was hardly eating anything so he didn't get upset, it was all getting a bit much for both of us so I gave in and let him eat. Worked out great here.
His reflux was at it's worst at that time, I'd only just got him an appointment with the paediatrician and been prescribed meds so I can't really say if it helped or didn't but when I told the paediatrician a month later that I'd started him a bit early she didn't bat an eye and seemed very positive about it. Two things I found - raw pear made him reflux which was a huge surprise as pear is one of the friendliest foods, and I had to be careful how much water he took, large drinks of water came right back up. You'll catch on pretty fast to things like that though.
I made baked wedges of apple, potato, sweet potato etc as they are dryish on the outside so easy to pick up but very soft on the inside.