What's vocaloids about?

First of all, vocaloids are voice synthesizer programs. You can make a melody and have the vocaloid sing for you. There are English vocaloids like Leon and Lola, Japanese ones like Miku Hatsune and KAITO, and Bilingual ones like Prima and Megurinne Luka.
As for the age,, it really depends on the song. There are a lot of really cute songs like Miku Ni Shite Ageru and True My heart, funny songs like Triple Baka and No Thanks. But there are some disturbing videos, like Fear Garden and Dark Woods Circus and sometimes Trick and Treat. Also some explicit (not naming). In the end, it all goes down to the video and the song. So in general, yes, it's appropriate.

Yeah its a program only avalable in Japan I think but idk

yup, 13 years old is fine. im 13, though, i fu don;t like gay songs, stay alway from "SPICE!" and some r creepy, like "Alice human sacrafice" but its ok. i thik u already got the answer for wat edsatly vocaloid is.

Vocaloid is a sound synthesizer program developed by Yamaha Corporation. Basically, it's just electronic music sung by computer-generated personas, the "Vocaloids". Vocaloid's mostly appropriate for a 13-year-old, especially if they don't understand Japanese... but some songs are kinda creepy...

well vocaloid is a singing software but you can basically enter in tone,melody,and other as well as lyrics to create a song with a vocaloid or if you want to its kinda hard though is to create a vocaloid of your own with a voice bank and everything but all vocaloid stuff are made by fans just like me so i'm working on 10 different vocaloid ideas now but i think inunutfan gave a good description to

There just a computer program, voice synthesizers, looks like you've got some decent answers but if you really want to know a lot about all the different Vocaloids try their wiki
link
There are currently 34 different Vocaloids singing in Japanese, English, Korean, Spanish, and Chinese
Currently 4 more vocaloids are in the making and they are updating many of the existing vocaloids voice banks. The most popular vocaloids are Miku, Rin+Len, Gumi, Gackupo, Kaito, Luka, and Meiko.
I gotta get out of the house more..... ^^" cause that was all by memory....