This was my grandfather's first name, but he went by his middle, and is my uncle's first name. He went by Freddie as a boy and goes by Fred as an adult. While I love it, especially for the family connection (I have very few blood relatives) I took it off my list for my son, since Fred/Freddie/Freddy would feel confusing with my uncle using the name. My grandma wanted me to name the baby Frederick nn Rick, but I really dislike Rick, so I'm using my grandfather and uncle's middle name instead, since no one's currently using it.
Also, at my LLL meetings, there's a 3 month old named Frederick, so I've seen it work on a little baby as well as on a grown man.
Thanks, everyone! I'm adding Frederick to my list. :)