I don't believe you can rent snowmobiles on the mountain. However you may be able to at The Resort at Squaw Creek nearby or at local companies in Truckee. Most likely need to be 18 to operate one but should be able to ride with an adult.
Zach is correct. No snowmobiling at Squaw Valley or any of the other ski resorts in the area. But, there are a couple of companies around to rent snowmobiles. In Stateline Nevada on the south shore of the lake, there is a small mom and pops place that rents snowmobiles to ride around a track, and they also have a tubing hill. They are right across the street from the Mont Bleu Casino and Hotel
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