No. The operation itself is not the dangerous part. There is a very small chance of death from the operation but the more important issues is the long term implications. 16 year olds have. Along life ahead of them and they may develop kidney problems in the future. Also they cannot legally give consent so someone else is consenting for giving away their kidney. Ethically it is a wrong thing to do.
Yes, but no. A healthy 16-year-old can generally lose a kidney (to trauma, etc) with few long-term consequences, so donation should be safe. However, very few transplant programs will take a donor who cannot legally consent. Donation does have long-term risks, and even with the most altruistic motives, a 16-year-old should not be making this type of decision.