I wouldn't add that to the list of skills, if you wanted to include that you were a "fast learner" as you put it somewhere in an about section where you can drop in that your able to adapt to new concepts and systems.
My about section is short and sweet as it is now. To add more would only bring down it's value. Anyhow, I want to market to ability to learn quickly as a skill. Wherever I mention it is where I'll add something similiar to your "able to adapt to new concepts and systems"
"Fast learner" — definitely another bad one. Doubly so, because it combines desperation with ignorance; you wouldn't need to call it out if you could demonstrate something concrete that you've already learned. If you have some true demonstration that you're a fast learner, such as entering college at age 14, then sure, call it out. But the phrase "fast learner" is a fast track to the Big Resume Bin in the Sky.