If or rather when I turn 65 and start being covered by Medicare, can I deduct my premiums for Medicare from my taxes, provided I meet percentage requirements? Also, can I deduct secondary insurance premiums if I meet percentage?

Yes, you can deduct those premiums as itemized deductions.

ATE, do they have to pass the threshold for medical expenses?

Yes, but the OP seems to be aware of that requirement!

Aren't your medical costs deductible, any time, as long you meet the percent?

Yes, catonsville, but this person is asking about the premiums, which many people don't realize. Plus the Medicare premium is deducted from our SS checks. We never get a bill and many people don't even know how much it is.

Aren't your medical costs deductible, any time, as long you meet the percent?

That's what I wanted to make clear, That medical insurance premiums are lumped in with all medical expenses and, only if you meet the threshold can you deduct.

The premium ($1259) is on Form 1099-SA