Playtime or Potty time?

She has mastered the toilet. All except the actual act of going to the bathroom. She runs to the bathroom, tells me, "UP," and then proceeds to take all the toilet paper and place it in the bowl and then she flushes. multiple. times. When is it too early to start potty-training? I know I don't want things to "back-fire," but I also don't want her to get too comfortable and not want to use the toilet. I guess my strategy is to allow her to have fun and continue to ask her if she needs to use the potty when she's fiddling with her diaper. The other day she actually refused to wear her diaper and chose panties instead. I set my timer and after every 20 minutes asked her if she needed to go potty. After 40 minutes I knew I was bound to have an accident, and I did. After she saw and felt what she did she said, "I pee, pee." She gladly put her diaper back on.
Can I really get mad at this face? She definitely is growing up way too fast.