About age rating:
While Ranma 1/2 is usually innocent fun, multiple girls are shown uncovered and completely topless in this anime (sometimes we even see a rear end). As a female myself, I took this with a grain of salt and was not significantly affected by this since the scenes are not usually provocative in nature. Not to mention, the art style kept me from taking it seriously. I didn't want to over-rate the age ranking and turn people off of this particular anime, since its intended audience would be younger teen girls (it is a shoujo series, after all). That said, this anime is not recommended for those negatively affected by the sight of bared female chests.

Please note: This is a review of the Viz English dub of the Ranma 1/2 series. The sub may have more language issues.

Violence / Gore:
Ranma and multiple other characters in this anime constantly fight in martial art battles. There is little to no blood shown. There is a great deal of comedy violence as well, i.e. characters getting hit with tables and tea kettles.

Nudity / Sexual Content:
As mentioned above, this anime shows female chests (uncovered) multiple times. There are multiple bathhouse scenes in which characters run around half-covered or nude. Ranma tends to run around naked in his female form because he's a guy and doesn't care about being modest.
Ranma constantly changes gender. Though he does not like the fact that he changes into a girl when splashed with cold water, Ranma does use his female form to his advantage in fights, etc.
There are a couple of times when a character imagines "deflowering" a girl. This is shown figuratively (usually we see a flower losing a petal). Nothing graphic is ever shown, and nothing ever actually happens.
Note that Ranma is not lecherous nor sex-driven. His mind is usually on fighting and winning whatever battle or challenge he's gotten himself into. However, one recurring character (a kid-sized old man) is extremely lecherous. He tries to peek on women, steals underwear, and often tries to hug large-chested women.
Many male characters are in love with Ranma (whom they believe is a girl). This is portrayed as more comedic than anything else. Ranma sometimes toys with these guys to put a situation in his favor, but he does not have romantic feelings towards any of them. Again, these guys believe that Ranma is a girl, hence their behavior. Ranma generally employs comedic violence to get rid of them.
Ranma also has many female suitors, who want to kiss/marry him. These girls can dress skimpily. One girl is at one point willing to have her way with Ranma to make him hers. Nothing ever happens. Ranma's suitors mainly want his undying and undivided love and affection rather than anything physical.
Some males are also shown nude in this anime, though the important parts are always covered. This is another shot at comedy, and the guys are not trying to be sexual.
The Ranma 1/2 movies are generally more detailed art-wise and seem more provocative than the series itself.

Potentially problematic theological themes:
Ranma (and many others) fell into a "cursed" spring. They magically change form when doused with cold water. This happens very. very often. There are various attempts to find a magical cure to the curses. There are also various monsters in this anime, some with powers.

Other potentially problematic themes:
Random, mild swearing. Not too often in the dub. A few times where characters seem tipsy.

* Ranma 1/2 is a rambunctious laugh from beginning to end, but it has its flaws. While the many characters are unforgettable, some of them are downright annoying. That said, the adorable almost-romance between Ranma and Akane is worth the time investment (in my humble opinion). Ranma's shy-and-stubborn attitude is much like the main character from Inuyasha, which was written by the same author as Ranma 1/2. Shoujo fans will likely find Ranma charmingly (and humorously) entertaining.