Aw, there is so much conflicting advice, it's so easy to get confused!
Ok, well read here first:
http://babywhispererforums.com/index.php?topic=36922.0The WHO recommendations are just one recommendation, they actually vary all over the world and from different organizations. So don't worry about just that one.
How is your LO doing with the cereal? Does he enjoy it? Is it upsetting his tummy at all?
I would say one of the biggest concerns for waiting until 6mos is giving your LO's digestive system time to fully mature and for his leaky gut to close. But if he is enjoying it and doing fine, then obviously that is not an issue.
I tend to lean towards waiting closer to 6mos, but that's because in my recent experience my baby wasn't ready early and he had a sensitive tummy. This is not the case with all babies. It really depends on your baby. Babies don't read or follow recommendations, some will be ready earlier than 6mos and some later. My DS1 was good to go at 5.5mos, but my DS2 took well over 6mos to be ready. The important part is that you are listening to your baby. If he is enjoying it and all is good, then by all means continue. But if you notice he just doesn't seem that interested, then stop for now and try again at 6mos.