Be what you want to be. Do what you want to do.
There is really no other option. You won't have the psychological energy to succeed any other way. Doing what someone else wants leads to a wasted life.
There is no such thing as "being boring." Boring is relative. Subjective. If you do what you want, you won't be boring to you, and that is all that matters.
The advice you've received, in this particular instance, is very toxic. Unless your mentor is saying: Don't do what is boring to you. Then, maybe it's valid.