I'd like to take martial art lessons over summer vacation, just for fun and it'd be good to learn.
I'll put this in bold: I DO NOT expect to be somekind of Black belt/unstoppable killing machine after summer vacation.
Putting "martial arts lessons over the summer" in the same context as "be some kind of black belt / unstoppable klling machine"
is like putting together "making a souflé" and "egging a house on hallowe'en,"
they both use eggs but other than that there is no relationship.
Projecting your fantasies on the reples here, even in the negative, suggests you get a Sensei over 45 years old who does not do tournaments.
"Fear, not compassion, restrains the wicked."