Based on the facts you provided, he could be charged for Trespass under MCL 750.552(1)(a). On the other hand, if he is charged with Illegal Entry under 750.115, he may have a defense if his purpose in entering the premises was to retrieve property that belonged to him.
At age 17, he is considered to be an adult for charging purposes. Clearly this is a complicated issue that should be handled by a competent and experienced attorney.
The prosecutor will have a difficult time proving the necessary element of 'intent' aka as "mens rae"
You (he) will need a good criminal defense attorney in Michigan to help you keep this charge from moving forward and blemish his record for the rest of his life.
Contact Attorney Daniel Hajji for a consultation. There is no charge for this consultation.