For oatmeal, I found the Healthy Times oats cereal a really nice consistency for early eaters, as you can make it really watery and it's not lumpy. For Quaker Oats and other adult oatmeal, I really never started to give that to my son until he was a few months older - I think 10 months or so.
If he's not keen on the solids though, since he's still young, it might not hurt to wait another week or two before re-introducing them. I started my baby on solids at just before 5 months, but he was really keen(and need more sustenance than my milk) and still I only gave him plain rice cereal for the first few weeks just to ease him into it.