How you rate: 14 words, average; 19, good; 24, very good; 29, excellent.
Source: the Times
Answers on the post continuation (note, not in the comments!).
agate, age, awe, east, eat, est, eta, gate, get, sage, sate, sea, seat, set, seta, sew, stage, stew, swage, sweat, tawse, tea, teg, wage, waste, west, wet, weta
wastage is the word using all the letters.