|Jeremiah blesses Nephi as a kitten.|
Jeremiah is one that was called while still young. Daniel, Ezekiel, David, and others--these people were young when they performed much of their work. Why do we insist on giving them big gray beards all the time? In reality most of these people that have interacted with Deity were middle-aged or younger, including Jesus and John the Baptist, and if you're Mormon, let's not forget Joseph Smith. Get with the program people. Being young is cool. People over 30 are boring.
The "laying on of hands" was an established practice for blessing or conferring authority during Biblical times. Moses and numerous other prophets and patriarchs are recorded having done so.