Manu is 17months in the pic and the hair is still growing. This is his summer coat, it will get thicker in the winter. His chest hair was like this already before his first birthday, but the ears and the rest of the body had shorter hair until recently.
I've noticed that the black hair is better quality (more shine and smoother) than the grey spots. Frankie seems to have more black hair than grey already, so he should have very nice coat when he grows up!