"mind of " vs "mind like " which one is correct in the below context

To me both are correct but both bring different meanings:

1) It suggests that the mind is definitely a 12-year-old mind.

2) This somehow has that sound of not exactly having a definite 12-Year-Old mind all the time, maybe at a certain time like when a person acting like a child.

Saying "He has the mind of a 12-year-old" when you mean to indicate that he does not think like an adult is quite idiomatic, even if it's not something that anal-retentive linguistic purists would approve of. The only difference in common use is that "4-year-old" is more likely to be used.