Actually, DM is fairly common in young adults although older folks get it as well. I have polymyositis but lead a local support group for myositis diseases in the Chicago area and am quite familiar with the disease. I suggest that you post on the following sites and you will find many with DM who can answer your questions.
A closed group for DM and PM on Facebook. Just request to join and you will be admitted...it is open to anyone with PM or DM.
Let me know if you have any specific questions.
MCTD (SLE Lupus, polymyositis, scleroderma). Diagnosed 2005. Kidney, liver, GI tract, dysphagia, raynauds, barretts esophagus, quadriplegic in 2005. Recovered and now active in downhill skiing, golf, hiking. Meds: amlodipine, benezapril, omeprazole, potassium, folic acid, vitamins, maxide.
Remain Optimistic and you can overcome.