My son is 24 and not a listed as a depended on our taxes. He is covered by my health insurance however. Can I deduct medical expenses related to him?

Possibly.  There are times when you can deduct medical expenses for someone who is not listed as a dependent on your return.  In order to do that the following would have to apply:

• "He lived with you for the entire year as a member of your household.
• He is related to you (as described in the section  Who's a Relative).
• He was a U.S. citizen or legal resident, or was a resident of Canada or Mexico, for some part of the year.
• You provided over half of his or her support for the year."

https://turbotax.intuit.com/tax-tips/family/tax-exemptions-and-deductions-for-families/L0Nx5Tnxi  Click on link for more information

If all of the above apply, then you can deduct his medical expenses.  

However, please note, that if he is covered through a plan through your employer, generally, insurance paid through an employer is not deductible as it is paid with money you are not being taxed on so it would be considered double dipping. So the premiums paid would not be able to be deducted although other eligible medical expenses would be.