What is the ruling on young men and old men kissing each other on the cheeks, and that being in the mosque, and what is the ruling on kissing on the shoulder?

The Sunnah is for a Muslim to shake hands with his Muslim brother upon their usual meeting. There is no harm in embracing and kissing on special occasions, but these are disliked without an occasion. One must be careful that kissing or embracing between young men is not out of lust, as that is one of the greatest causes of temptation. If kissing on the cheek is permissible, then it is even more so permissible on the shoulder.