The use of one's thumb and index finger to grab something is called the "pincer grasp." Babies normally develop this between 7 and 11 months.
I hit this milestone *very* early, and have been using my pincer grasp since I was 3 months old. Since then, I have very deliberately picked up small objects with my thumb and index finger and maneuvered them. Mommy thinks that my early pincer grasp development means I will be uniquely qualified to perform neurosurgery, but made it a point to tell me that any surgical specialty I choose is just fine with her. That's good to know, mommy!