I agree, there is no such thing as normal when it comes to babies!! My daughter is 16 months, has all four teeth at the top, all her first molars and is cutting her canines at the moment but still is missing one of the first four from the bottom! It just doesn't seem to want to make an appearance! Lol! Don't worry about it hun. xx
The fact that you son has teeth at 6 months is a great start, nothing is "normal" in baby land, they are all so different. If he gets to 18 (years) and you still have the same problem then worry ;-)
my son is 6 months old and has 4 teeth, he has 2 on the top and 2 on the bottom. he hasnt cut his 2 front teeth he has cut the ones either side,, i showed my health visitor and she said she hasnt ever seen a baby cut those 2 before the front ones. is it normal? i think its quite quirky but a little weird