Yeah, no one knows what 13th or 14th gear mean, because we have no idea what crank and cassette you have or which side you are counting from for that matter. Gears are designated by the combination of front ring teeth divided by rear cassette teeth as in 53/19 (or this number time the diameter of your wheel, so called gear inches). But it is most common to say something like, "I was riding the 53/19." That is perfectly clear with no ambiguity on a 700c wheel bike. In flat land Houston I normally ride a four gear range 39/19, 39/17, 39/15 and very rarely 39/14. That gives me speeds at cadence similar to yours of about 14 to 22 mph. But for me it is not about leg strength. Between a heart attack and the follow-up meds I just don't have the wind anymore.