What medical or other benefits do reservists have after retirement and how early can retirement pay be claimed?

The benefit package on Reserve Retirements after age 60 mirrors the Active Service. You will qualify for Tricare, you should have Space A and Commissary Privilege's as a Gray Area Retire already.

A member is generally not eligible for Reserve (non-regular) retired pay until they reach age 6o. However, any member of the Ready Reserve who is recalled to active duty or, in response to a national emergency, is called to certain active service after January 28, 2008, shall have the age 60 requirement reduced by 3 months for each cumulative period of 90 days so performed in any fiscal year after that date.

https://militarypay.defense.gov/Pay/Retirement/Reserve.aspx