perjury

Respected scholars, As-salamu `alaykum. There is a man who swore in a court saying, " I swear by Allah that the age of my son is 15 years." But he knew that his son is actually 16 and a half years old, but he did not mention the actual age because he sought the interest of this son in another matter. Is there any expiation for this false oath? Jazakum Allahu khayran.