I find with gifted children that relationships are flexible. Friendships can be formed with much younger, much older, or even adult peers. Gifted children are looking for a "safe shelter", a place where they can finally rest from the stresses of just being who they are. . . They may find this in many different forms. I don't typically see gifted children having only one best buddy. They have a variety of friends who serve a variety of purposes, because they themselves have unqiue and special needs for companions.
As a parent, you can encourage your gifted child to interact with all different types of people. Find people who match their interests- chess partners, crossword puzzle groups, or even preschoolers who also still like to pretend. Being broad-minded (while still being safe and aware) about their peers may be the key to finding their special relationships and freeing them from isolation and loneliness. . .