Vibrato is a skill that you can hone for many years. You can learn the technique in a few months, but it can take a while to perfect it. When I was first learning, it took me a month or so to figure out how to move my hand the right way. Then my teacher worked with me for another month or two, to learn how to relax my fingers, hand and wrist, so I was using more of my wrist and arm. The more I worked on it, the more my vibrato sounded more fluid, and not jerky or forced, and I was more comfortable doing it faster or slower, and following the feel of the music. When I eventually stopped playing after 8 years, I knew my technique still wasn’t the best, but it was pretty good. The key is practice, practice.