Q:

My interest in 'x' CULTIVATED many years ago...?

Is there anything wrong with saying the following?
My interest in Japan cultivated many years ago after taking part in .....
I initially used the verb stemmed as I want to indicate that it began after taking part in '...', but I was told it did not make sense.

A:

I think you have to say "My interest in Japan was cultivated many [...]".
If you use only the word "cultivate", that would be the active version. For instance, you would say "I have cultivated my friends interest in politics" to express that YOU made him care about it.
You however want to express that your interest was cultivated and thereby grew bigger, not that your interest cultivated something.

