Your friend should ASAP consult with a Criminal Defense attorney in the locale where they pled in New York to discuss their "expungement" options -- in Michigan, one must file the Application for Order Setting Aside Conviction (i.e., an expungement) in the Court where they pled. Good luck.
I agree with the previous answer, but just to add to it and clarify a little bit: in Michigan it is not automatically erased from your record. Your friend cannot honestly state that he has not been convicted of a felony until he investigates further.
In most jurisdictions juveniles are not “convicted” of a crime but are adjudicated delinquent. I would suggest that your friend also ask the Criminal Defense attorney in New York whether he were actually convicted. If not, then he can truthfully state that he has never been convicted of a crime.
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One more answer for you. In Michigan, a person is treated as an adult for his or her crimes beginning at age 17. I have many clients who say that they were convicted of something as a minor or juvenile but really they have an adult conviction because the person was age 17 or older when the offense occurred. That aside, I do not know of any statute in Michigan that erases a juvenile delinquent conviction at a certain age. However, some offenses are handled in Michigan by "diversion" or "consent calendar" which is the best case scenario and no entry of guilt or adjudication is entered on the juvenile record. This is a situation where you can retain a Michigan attorney to make inquiries on your behalf to the state where the case was heard. Otherwise, your friend can hire a lawyer in the state where this issue is present for expungement or to provide him with an answer regarding how records are treated.
The bottom line is that records never completely vanish. They may be sealed or become a non-public record. However, even non-public records have a way of surfacing.