Maybe it's small edit help you:

Than I want to say about form of face (light, shadow) and contrast... also about his smile

(he is too sad). I don't edit type this face too much, because that's you choice! But if you paint man, than he not impede a more manly chin and cheek-bone. This type face of young man (15-17 years).
For girl: Paint here more large in this size, as a man. And how make her sexy? Paint as
here in pixel, for a start, with comment other people. Because now she is a faceless, but something in her prettily )))
And... good luck!