I learnt to play clarinet before sax, from the age of 11. By the time I took up the sax at 15 I was pretty proficient on the clarinet, and I found myself immediately at home on the sax. It's not so easy the other way round. Not only does the clarinet have a small reed and mouthpiece, but it overblows in twelfths, not octaves. So, on a sax when you press the octave key, you go up an octave, and the fingerings are otherwise the same. On a clarinet the 'octave' key takes you up an octave and a half. So, one set of fingerings much the same as the sax, one completely different.
Having said all this, to actually anser your question, if you can play a clarinet you can probably play a sax without too much trouble. You'll certainly be able to pick up the sax far more quickly than someone new to woodwinds. Particularly since the sax is a far, far nicer instrument, with much better music to play. The sax just makes me want to play music much more than the clarinet does.
Jon