Anwar al-Buni, a lawyer of the Human Rights Association of Syria, said on Monday their release was ordered by Juvenile Court, to which they had been referred after their arrest.
Adult detainees were referred to State Security Court, which tries political cases.
Nearly 2000 Kurds were rounded up during the March clashes between Kurdish rioters and Syrian security forces that left 25 people dead and more than 100 injured. Many of the detainees since have been released.
The clashes erupted following a brawl at a soccer match in the northeastern city of Qamishli and later extended to Hasaka, capital of the northern Hasaka province. The two cities have large Kurdish communities.
Al-Buni said the charges against the youths had included damaging public property, fomenting riot, harming national sentiments, confronting policemen and directing insults and abuse at Syrian authorities.
He called their release "a positive move" and urged authorities to transfer other detainees to ordinary courts, instead of the State Security Court, and to stop all kinds of political detentions.
Decisions of the State Security Court, set up in line with Syria's 1963 emergency law, cannot be appealed and the cases often are heard by military personnel rather than civilian judges.
Syrian Kurds long have complained they lack basic rights, and that the areas of northern Syria where they live are neglected by the government.
About 1.5 million Kurds are among Syria's 18.5 million population. More than 10% of them, about 160,000, are denied Syrian citizenship.