Would you be kind enough to tell me your opinion concerning the following two sentences?
1. He is serving ten year sentence.
2. He is doing his stretch of ten years.
Thank you for your efforts.
Either sentence is correct, and both describe the same scenario: a prisoner has been sentenced to serve 10 years in prison. "Doing a stretch of 10 years" (also often phrased as "doing a 10 year stretch") is far more colloquial, but it is pretty much universally understood.