No, not possible.
A poly grad would already be 20 by the time he graduates from poly
and enlists.. since he'll have to ORD before going uni, that'll
mean that he'll be around 22 by the time he enters uni, at least.
Assuming that he graduates in 3 years time, that'll mean 25 upon
re-renlistment. And upon re-renlistment, he's only an LTA..
CPT possible, but definitely not MAJ.