nuts about, be - Phrases/Idioms
The American Heritage® Dictionary of Idioms by Christine Ammer. Copyright © 2003, 1997 by The Christine Ammer 1992 Trust. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Be extremely enthusiastic; also, be extremely fond of. For example, Ellen is nuts about opera, or Kevin has been nuts about Megan since he met her. This seemingly new slangy expression began life in the late 1700s as nuts on or upon; about began to be substituted about 1940.