What's the % of 66 yr sentence

In most situations, there is a built-in good time credit of 15%. On 66 years, 85% is 56.1 years. If his sentence was in a state court (not federal), there is a chance that the judge in the case added a parole provision. If that is in their Judgement and Commitment Order, then they might be eligible for the first parole board meeting at 1/3 of their sentence.