It looks very similar to the girl's eye. The only real difference is that it is rounder and thinner.
The smoother the line, the more it enhances the character's naivety.
Then you have to draw the inside of the eye. The outline can be thinner than for a girl and the pupil is larger.
Draw a reflection on the eye.
The eyebrow should be smaller, but thicker, to show his youthful energy.