No direct experience.
However my DD goes to an all girl's prep school and will go on to all girl's high school.
Many of her friends have brothers who are already at, or due to go to, the all boy's schools.
We also have a few friends who have been to single sex schools, who are now adults.
All are normal! All mix well with both genders. None are obsessed with the other sex, and all manage to make normal relationships with males and females.
My DD does not have any siblings, but she still sees and mixes with boys - at swimming, at trampolining and socially - family friends have boys. DD has no problem playing with boys at all so far, and this is despite being a very girly girl.
How they grow up is very much dependent on many other factors, not just their schooling. If you as parents make sure your child grows up with a normal and healthy attitude to the opposite sex, and ensure they do occasionally meet the opposite sex, then they will be fine!