9 weeks old is fine to start feeding small silkworms. And because silkworms have such soft bodies, you can feed the cham worms that are slightly larger than the size of cricket you are currently feeding it.
Of course, there is no guarantee that your cham will actually eat the worm. Some chams are fussy eaters, and the slow moving silkworms don't always attract their attention. But chameleons' preferences do change over time (and possibly with the seasons): if it ignores the silkworms now, that doesn't mean it won't enjoy silkworms in a few months time.
As for feeding greens, they usually only become omnivorous as sub-adults (so from about 6-8 months), so it is quite likely that your cham will ignore the greens for some time still.