Light weight formula
Ive been sailing formula for the past 3 seasons and weigh 65kgs. Ive been able to sail most of the races with a 10.0m race sail. There are occasionally times when I do need the 10.7 and 9.0 sail as well. Usually when I need the 10.7 the racing is called off as no one else is planning.
A 9.5m RSX sail might be good to get started on but he might feel a little underpowered after a while.