Learning to play the violin can be done at any age since learning any new skill has more to do with your desire, determination and discipline than with your age and the violin is no different. It might be easier for children to learn since they are able to adapt to the instrument quicker, but that doesn’t mean that an adult can’t do it.
As stated above, you can make up for that with enough determination and discipline. Older students have the advantage in the discipline department and once you take that into account, the advantage that younger people have becomes negligible.
What’s important is to find a learning style since each person learns differently. Some people prefer to incorporate information through reading or listening, while others benefit more from hands-on activities. Once you figure out the best learning style with your music instructor and you begin to focus on practicing, you’ll start  to notice improvements very quickly.