the "The mind is a sponge" thing is valid up to about 5 years old so no, there's not much of a difference learning guitar as an adult or child.

It may be a little harder as an adult to learn guitar because there's work and aging begins (losing brain cells), not to mention weird diets that really affect your intellect, and, in my case, too many hobbies to have enough time to properly learn guitar.

I guess the best thing to do is to focus and set goals over a few weeks/months and see how you progress just like you did in grade school. You can avoid dating, too, yeah, you know you're all messed up when you start to have feelings for someone.