Avril was born in Jacksonville, Florida, to Haitian parents. He attended Clay High School in Green Cove Springs, Florida, where he was a four-sport star in football, track and field, weightlifting, and basketball. Avril was an All State player in basketball and football. He was an All-conference selection his junior year. As a senior in 2004, he was a second-team All-state selection and was named to The Florida Times-Union Super 24 team after recording 80 tackles, including 11 for loss and nine sacks, with four pass breakups, leading his team to an 11-2 record.
In 2004, he appeared in all 12 games, including four starts made 36 tackles (23 solo, 13 assists), including 3.0 for loss and 0.5 sacks, with one pass breakup and one forced fumble. In 2005, he appeared in 10 games, including four starts and had 33 tackles (21 solo, 12 assists), including 2.5 for loss. In 2006, he started all 14 games, the first four at linebacker and last 10 at defensive end and recorded 84 tackles (51 solo, 33 assists) 15.0 tackles-for-loss, six sacks and six pass breakups, two forced fumbles, one fumble recovery and one interception.