The unargued, unsupported association of youth with uncultured frivolity is not merely parochial: it’s a sad place to be yelling from, especially if you’re playing life on the lowest difficulty setting.
Are you saying his argument isn’t valid based on his race, gender, and sexual orientation? If the argument was about these actual issues and if the arguer dismissed the inherent privileges therein, I might understand why this was brought up. But for an argument that has nothing to do with race, gender, or sexual orientation, bringing up the “lowest difficulty setting” argument is pretty much saying that you have dismissed a person’s argument based on your stereotype that their life has been easy.