General rules.
Second Life is, generally speaking, very sex-positive and open-minded. There is really just one taboo: No kids. However, there are content ratings, General, Moderate, and Adult. While Moderate areas are good for your house and whatever you’d do in private with a committed partner(s), it requires an Adult-rated sim to do stuff out in the open. Second Life adult areas can get pretty wild in themes, and you should spend some time to find the eact right kink for you.
Second Life does not allow minors under 16 years old to join the platform AT ALL, and 16-17-year-olds are only allowed in Moderate areas. In my years on Second Life, I have encountered ONE person who I suspected not to be quite of age, so it’s not very common to find anyone under 25. Ironically, given that Second Life is a little “childish,” it quite naturally does not attract peopl who still have to consciously “act adult” to feel like one. :p Once you can buy a Barbie doll or a train kit without feeling like a child… You’re ready.
There is such a thing as good and bad SL sex.
Although nothing beats natural chemistry that allows for all kinds of noob mistakes, sadly or gladly, depending on your perspective, there is such a thing as good and bad sex in Second Life, too. There is a learning curve, so you can actually become technically good at it – but on the other hand, understandably, you may struggle at first. (Understanding the basics of how to animate and adjust animation positions is the first key.)
If you don’t care for the whole animation thing and stuff, don’t do it. It’s better you don’t do the animation part and only talk about sex (which is more than fine) than to do it half-heartedly with a CACACA: Crappy attitude, crappy avatar, and crappy animations.
SL sex is FAR from intuitive. 😀 You actually have to become good at it to make it pleasurable. You add a new tool, and your experience flies out the window. :p You stick to your old toys, and you’re fast bored.
HERE ARE A FEW TIPS:
SEX OUTFITS are your sex life savers!
When things get started, you don’t 
want to be fumbling looking for your cock or vag HUDs and outfits and alpha layer HUDs in your inventory while hovering in the air in a weird half-sitting pose because your Animation Overrides are still on. Therefore, have an outfit saved for “Sex ready” and perhaps name it #Sex Ready, so you’ll find it in a heartbeat at the top of your Outfits Inventory. In it, store your avatar naked (or in whatever you wear for these things), with all the HUDs (control panels) you need to make a fast transition from clothed to nude: your cock hud, and your mesh avatar alpha cutter, so you can fast “show all” skin parts. Take some time to make your avatar ready for action, and save the whole thing as an outfit.
Practice switching to nude fast. You know why. 😉
If you’re a super nerd, ;p store two versions of your avatar: a giant (well over 2 meters) and a normal-sized (1.70-2.05 for males and 1.50-1.78 for women) version to match people who don’t do this and play a different scale than you do. It is, generally speaking, not a good thing if the male is A LOT larger than the female, although it does cater to some giant-fetishes. The best animations are motion capture, which means they were acted out by real people. This, in turn, means that it is UNLIKELY the height difference between the actors was more than 0.30 meters. (A head taller male.) (Also read “how tall am I supposed to be?!“)
Store the two versions of your avi as different outfits. (No need to buy a smaller avatar for this, in fact, you couldn’t if you tried, just resize your favorite avatar’s shape and make sure you name it differently from the original so you can store and use them in different outfits.)
RESTRICTED LOVE VIEWER (RLV)
Nothing here happens by accident. For instance, there’s such a thing as RLV, Restricted Love Viewer, meaning that you take part in abduction/forced sex role play, but to make yourself available for forcing takes a freak ton of effort on the victim’s part.
It is good to know, too, that if you’re able to grab a girl (or a guy, for that matter) for sex by using RLV, they’ve consented to it, and you don’t have to ask. The RLV relay can be configured to “off,” “ask,” or “auto-accept,” which means that if you CAN’T technically do it to anyone without their permission.
I personally have my RLV stuff configured, and it wasn’t freaking easy. Still, usually, I have to advise the kidnapper on how to rape me, which is not ideal. ;p Hence, check the rest of this topic on ‘functions.’ (If you’re into this sort of thing, ask someone (like me) in a relevant adult group to practice the technical aspects with you. Troubleshooting can also lead to all kinds of situations… :p )
However, ONE THING I would check. The RLV typically doesn’t check for the sexual orientation of the participants. Therefore, if you are a nice rapist, you’ll check the person’s profile for clues about whether they’re gay, bi, or straight before you grab them, although the location you find them on will give you a clue, too.
A TRAINING PARTNER
You may be curious about how the other side lives, as in, what the opposite gender partner has to go through when they’re having Second Life sex. You might want to try using a cock/vagina menu, navigating Use Me -tools, or Mama Alpha; how does RLV-gear work for the other partner, let alone whether or not your collar remote actually works…
All of that stuff could be tested and tried out with an alternative avatar (alt) that you log in with using another computer or an instance of Fire Storm. (You can run two copies of the viewers simultaneously and be logged in on two accounts if your network and computer can handle the load. For this purpose, if you can run SL on a crowded sim without crashing, you should be well able to set up a monogamous test session. :p)
This will help you help an actual playmate if they are struggling with their functions during play.
DON’T PRETEND TO LIKE WHAT YOU DON’T REALLY LIKE TO GET INTO
A lot of people here are into role-play (RP). Obviously, given the platform, it’s no surprise. There are several levels of it: Pretending to be you but not where you are and not exactly in the right body, using animations as a visual while you have a sexy discussion somewhat unrelated, while not minding too much what happens with the avatars, and perhaps using the animations somewhat as a discussion point.
Animating and emoting (typing out the actions and “feels” to your partner) and then taking part in organized role-play sessions with full-blown scripts and characters involved. Trust me, there will be people who will be relieved you’re not fully into something that they feel is a lot of work, and vice versa. Obviously, it’ll be difficult to find good role players, so if you’re into that, go full-on, right?
What one person like isn’t what another person likes. Don’t bother pretending; you don’t know if you’re both pretending to be right into something that you’ve found to be a Second Life standard and would find it a relief not to do that. Nothing wrong with trying out things you haven’t tried before, obviously, even if you don’t know if you’ll enjoy them or not.
Now, go out there and identify as a digisexual Second Life avatar and demand respect. :p