Is it better to learn a musical instrument when you are mentally ready?

I am thinking of learning to play the piano.

However, I am an obese person. And I tend to feel lethargic and feel uncomfortable if I sit on a bench for some time. I feel that I will not be able to focus on learning and practicing due to this.

I am thinking of losing some weight first (around 10 kg) and then start learning the piano because I feel that I will be more comfortable and more confident in playing the piano.

However, it will take a 2 - 3 months for me to lose 10kg. And I feel guilty/annoyed (not sure how to describe my actual feeling) that I am "postponing" my learning.