Can a non collegent athlete coach high school team?

Generally, no. Most high school athletic associations have rules requiring coaches to meet certain qualifications, and a college degree is often a requirement, or at least strongly preferred. While specific rules vary by state and even by school district, lacking a college degree would significantly limit the possibility of being hired as a head coach. They might be able to assist or volunteer in some capacity under the supervision of a qualified coach, but leading a team independently is highly unlikely.