No offense, but I don’t think you understand American Beauty and the reason why Nick loves that film.
It’s not about the underage sex, it’s about freedom. Freedom from his stupid wife. Freedom from his five annoying kids.
Nick wants the freedom of cutting all that out of his life, and live the live he never got to have in his 20ies. Goofing, partying, doing drugs.
At some level he’s too scared of the price associated (alimony, child support, family cutting his trust fund, public perception, etc.)
So he admires Lester in the movie and dreams about doing it. And has to settle for isolating himself in his “office” while the kids starve, and get the wive to go along with the lovely April moving in and as his personal groupie/fleshlight.