Originally Posted by Satai
I think the reason you've been told this is that the violin is such a small instrument, that some people find it easier to play when they are younger (and have small hands), rather then that you can't learn.
I can understand someone saying this, especially if they want them to buy a more expensive instrument!
If this is the case, violins do come in different sizes. I started out with a 3/4, but now I have a 4/4, or full violin. But they measure your arm at a professional shop to make sure you're getting the right size, if the possibility of needing a smaller one is an issue.
Violas are a little bigger, but they don't play in treble cleft, so you have different sound. I guess if size was an issue you could try viola, but only by a little. But I don't have a viola, so don't take my word for it
ETA: Satai mentioned RSI, and I wanted to add that I do have some shoulder and neck issues that started when I was active in volleyball that really took a toll on me when I was playing my violin the most, (in two orchestras and daily practice!) so it is a concern if you already have some issues to get a good pain management plan with your doctor now, lol.