From memory the optimum weight for a Starling is 65Kg with minimum entry weight considered as 55kg. When my daughter was sailing there were a few trying to sail at 50kg but they really struggled in the heavier conditions. Having said that the girl that was previously sailing my daughters boat was just over 50kg and had developed techniques to cope and was very competitive. They boys she was sailing against really started to become noncompetitive at around 70-75 kg depending on their skill level.
I don't know much about the Lasers other than there are three rig sizes - 4.7, radial and fu