I learn from others in groups mostly. I've not had one single dedicated professional mentor but frankly, I don't think "simply having a mentor" is necessarily of much value. Obviously, it would depend greatly on the mentor and their actual skills as well as their skills and desire to teach. I think that having a mentor who is unmotivated, teaches bad habits, etc... is actually worse than having no mentor at all.
Now, if I was able to work under the wing of a guy like Uncle Bob Martin, Jonathan Blow, Casey Muratori, Landy Wang, or Anders Hejlsberg for a year, then of course that would be another story.