“It is forbidden to teach a gentile Torah, as was said, ‘He did not do so for any nation’” (Hagigah 13a).
According to what Baal HaSulam interprets concerning prohibitions, wherever it is written “forbidden,” it means impossible. It follows that the prohibition to teach a gentile Torah, even if he has been circumcised but does not observe the commandments of the Torah, is that he cannot learn Torah.
The thing is that there is Torah and there is wisdom.