Schwinn frame measurements are center to top, which is inflated about 1" (2.54cm) over the center to center measurements used by some others. With that in mind, up until 1970 the largest Varsity frame size (according to Schwinn) was 23" (58cm). For 1971 the largest available Varsity frame size increased to 24" (61cm), and from 1972 through 1982 the largest size was increased to 26" (66cm). Finally from '83 through '85 the largest size was reduced to only 22" (56cm).

From the size it would look like you have a '72 through '82 model.