I have a just off a 6 year gap between my number 3 and 4 sons.
It has worked out well for us although I have gone on to have a number 5 because I was worried about number 4 basically growing up alone.
I was able to focus alot on him because when the older boys were at school he was an "only" child.
He has grown up fast though and he is a very mature 3yr old now. He wants to be like the older boys and doesnt understand why he cant do the things they are.

It can be difficult at times for me to change my parenting cap from teenage Mum to toddler mum but its all a learning process.

Overall I have no problems with the age gap.