Is it safe for my 10 year old to use my elliptical?

Mistakes can be made at any age. In my opinion, any use of power tools by a minor should be done under constant supervision and use restricted to such times. Even then, there may be injuries. Work tools and power tools create hundreds of thousands of injuries EVERY YEAR. There are safety practices to follow when using tools. Flesh is unforgiving of the mistakes made by people using tools. A moment of inattention, a decision to do without safety goggles or gloves, an unexpected failure of material all can yield permanent injury. Here is an alternative question. At what age will the novice actually consistently practice work safe procedures?

Ask a doctor.