Hi!
My 2 month old son weighs 7.2kg and when I've tried to measure him I think he is about 68cm length wise. HV and GP are not concerned, they said you can't overfeed a breastfed baby but it seems excessive to me. Has anyone's baby been this big at this age? 
He's also had his thyroid checked for a different reason and there was nothing wrong with the results.