This is not surprising, violin technique is deeply rooted in the body (especially bow technique) and is difficult to learn past adolescence because your body/brain cannot adapt as well in adulthood.
Source: I learned violin around age 13 after already reaching an "expert non-professional" level in piano, found it very challenging and eventually gave it up after seven years of study.
Source: I learned violin around age 13 after already reaching an "expert non-professional" level in piano, found it very challenging and eventually gave it up after seven years of study.