Word for inability to think in certain ways

I'd say given person's mind is boxed in. That's where thinking outside the box becomes essential.

The best word I can think of, and which is often used in a humorous sense, is impaired.

OED. humorous. Lacking or deficient in the attribute or field specified. eg. from OED: knowledge impaired, humour impaired, financially impaired

Another good example and a personal favourite is irony-impaired.

I think "predisposed" can be used to show how a person is preconditioned or not-conditioned to do a certain act. To answer your question - example - Since Tim's parents are musicians, he can assumed to be predisposed with musical skills.

Another word which comes to my mind is "Knack". It can be used to show how someone has a specific talent. Again as an example - Tim is good with musical instruments, and yet he doesn't have the knack to come up with original tunes like his brother has.