A teenager is person whom adults over 30 don't understand, but who is really perfectly ready for some of the rights and several of the responsibilities of an adult.
Teens and sex
Pretty much the only teenagers who don't have sex are Christians that want Abstinence, as well as many other very religious people, like Muslim teens. Many also are either Socially awkward, interested in romance but not sex or neither, or are just not very lucky. Most have begun to masturbate by the age of 14, and many have sex around the age of 14 or 15, sometimes earlier. In the highly unlikely event that a teenage girl becomes pregnant, abortions are available through outpatient and drive-thru clinics operated by Planned Parenthood. Contraception is better than abortion and teenagers of both sexes should learn about it. Teenage Girls should know how to avoid getting pregnant and teenage Boys should know how to prevent their partners becoming pregnant. Most schools have Sex education in America and other developed countries. In countries like Uganda, kids at 14 are already having babies constantly and often done with school, even married, but then again, that's the average age there.
Age for Sex
Of course, you can't post any media showing genitals of yourself as it is considered Child Porn by the government and people who see such pictures may make trouble for you like showing pictures to parents or teachers or threatening to do that. Never trust anyone you know only online. If anyone is using pictures of you to blackmail you go to the police. It is advised that preteens and younger teens don't have sex especially if they don't truly understand the bad effects that could come out of sex, like STDS.
Teens are waiting longer before their first Sex than used to happen a few years ago. They're more likely to be ready for it and comfortable with it when they do it. Teens and older people should feel comfortable about sex before they start doing it. Equally important teens and older people should feel comfortable about the person they're having sex with before they agree to it. American teens and European teens start sex at similar ages and do it equally often. American teens are more likely to become pregnant because they know less about contraception and about how to use contraceptives properly.  It's best to make sure you understand contraception before you start sex. Australian teens also are inclined to wait for their first sex and most have sex for the first time with a steady partner. 
Serious Relationships are often started more in College
There are still a great many who don't have sex until College. Many do not have very serious relationships in high school and wait to be more interested in very serious relationships that they are very devoted to, to have sex. Many are still teens at that time, being 18 or 19.
Things that people usually start doing at 18
People often start to vote at 18. At 18, in many European countries, people start driving. 18 is also usually when people start college. In many places, as this is around when you end high school, it is also when your mommy and daddy are no longer your legal guardian, though some places make exceptions to those who are married before 18. You also have the option of being an emancipated minor before 18. The army only allows those 18 and up in the United States.
Teenagers and Homosexuality
This is commonly the age where people find out their Homosexuality.
Are teenagers often Bullies
In shows which have a younger kids point of view, teens are often shown as bullies who pick on younger kids. However, rarely do teenagers even bother with much younger children, many even say they have an attachment (friendly) to their younger siblings and even work with younger children. However, if a teenager is picking on (tormenting) a younger child, they are either a complete coward or they are being a bit psychotic, or they're just confused and acting out their confusion. Teenage years can be very confusing, and trying to face confusion or conflict alone can be extremely difficult. If you're being bullied, or if you've been bullied and find yourself taking out your frustration on other people, you may find that sharing can help. If you are being bullied tell an adult you trust.
The media also commonly portrays teens as crackheads and potheads which is unfair as most aren't like that.
Common things that most teens like to do
- Surfing the web
- Doing online social websites
- Looking at clothes
- Looking at shoes