This show is pretty good when it comes to it in general. Each story gets better, and I also like how they bring in different heroes (including my favorite, Static).
Sexual content can get bad as femal characters tend to have revealing clothing, but unlike Teen Titans, it is commonly not looked at positively, except for the Flash likes the one who wears the most revealing, and Batman has somewhat of an emotion towards Wonder Woman.
Violence is tame and not encouraged often, only once does a character loose his tempor, and that is Superman when he battles Darkseid.
Other than that, it is good by not showing what other shows of its kind show as positive, but you do have insults and name calling. They do teach not to gossip (when a character gets angry at Supergirl, her father says "It isn't good to talk behind the back of someone with superhearing." He says it in a way as not to gossip period). At times characters fight just to fight, but it is rare.
In the end, I would say you should be at least thirteen to watch this show, but I really wouldn't recommend it for the most part (only certain episodes are good).