Yes, my son did that right about that age. I got a nursing necklace for him to play with. They are working on their dexterity and getting more interested in things, and the boob is just easy access. While I was waiting for my nursing necklace to arrive (these have a break away latch and big items for them to play with), I put some of those link toys together for a necklace. I don't really wear good necklaces yet, but I have been able to teach him to explore the necklace and not pull (too much).
He will still pinch once in awhile, and usually, I exclaim, "Ouch, that hurts Mommy." For awhile this was actually making him laugh, but I would move his hands away and distract him with tickling his feet.
Lately, my son (1) has even started unlatching, taking my boob in both hands and pinching or tweaking the nipple. He also will play with my bra or nipple of the side that he isn't eating from. I keep saying that I need to bring out the nursing necklace again, but he does it so rarely, and it is more his curiosity now, and he isn't hurting me.