A few months ago I received an email asking me to give advice about the career of an Italian tenor. This left me a bit speechless. Now I have a small amount to say.
If you are acquainted with a not too young tenor in Italy whom you like but who is not being particularly successful, then this is probably because his voice or technique does not approach the imagined Italian ideal for a tenor. Perhaps it is a lyric tenor voice that does not successfully push to dramatic. I was not told any of these things.
In this case I would advise to try elsewhere. Audition in Germany and Austria. The French like a lighter sound. Know thyself and match ones efforts to ones talents.
It is difficult to impossible to give generic advice of this kind. Perhaps there is a reason for the difficulty the individual is having.