A minor may read the Torah (in shul) and serve as interpreter but he may not lead the recitation of the Shema, serve as reader for the Shemoneh Esrei or duchen (deliver the priestly benediction). A person whose clothes are torn so that his flesh is visible may lead the recitation of the Shema and serve as interpreter but not read the Torah, lead Shemoneh Esrei or duchen. A blind person may lead the recitation of the Shema and serve as interpreter but Rabbi Yehuda says that a person who was born blind may not lead the Shema.
A kohein who has blemishes on his hands may not duchen. Rabbi Yehuda also prohibits a kohein whose hands are dyed because people will be distracted and stare.