No, you don't have to enter Medicare information anywhere. In the Health Insurance section, if you were covered by Medicare, you'd select that you were covered by insurance, and that you weren't covered by any of the plans that are shown on the list.
Note that if you were receiving Social Security Benefits, you'd enter your SSA-1099 in your return, and that might include Medicare premiums withheld from your benefit. If you had a W-2, medicare tax would be shown on it, but there's no place to enter Medicare benefits.