Starting at about your child's age, we gave up on playdates. DS is now 7, and we probably have had less than 20 play dates in his entire life. And they are never, ever part of a group. One-on-one only. And I still carefully supervise. When I was fretting about social skills, another wise parent of a PG kids told me, "If you put him in a situation where he is destined to fail - he'll learn social skills, but they won't be good ones. It's no more fair than putting a (neurotypical) toddler in a position where they have to read to be part of the fun. It's just not fair until he's emotionally, and developmentally ready."
Just for another perspective--we did not have this issue with DS, who tests pretty high. DD was a late bloomer socially and playdates, etc were harder when she was young. But I would not assume a highly gifted child can't do playdates due to giftedness. Personality is much more of a factor, IMO.
