BOSTON — Authorities say a Massachusetts man has been sentenced to 17 years in prison for sexually exploiting about 150 boys by posing as a 14-year-old girl and convincing them to send him nude photos and videos of themselves.Twenty-four-year-old Curtis Simoneau, of Framingham, was sentenced in federal court Monday after pleading guilty in June to coercion and enticement of a minor and possession of child pornography.