I hear many people say that you have to start to play the violin when you're very young, but I think age is not that important. What matters is how motivated one is and how much fun you can have with it! :-) Anyway, I'm enjoying every minute of my violin adventure.
I do record a video every month to keep track of my progress. It really helps me to see what I should work on and which things have improved already.
I also keep a violin diary on my website www.violinadventures.com.