I ask this question in OOC chat frequently. Now that I'm not in a guild with a strict 21+ age policy, I like knowing how old the people are that I'm playing with. For me, I like knowing. It helps me to know how to relate to the person.
For a friend of mine, this is a huge issue. My friend recently left a guild he was heavily involved in because he found out that they were no longer sticking with their 18+ policy. The thought of playing with children makes him very uncomfortable. I don't share his issues, possibly because my best friend in the world also happens to be my 17-year-old brother. But I can understand how others might find this to be an issue.
The man behind the mask - real life ages in RP settings
RP is where real age can be the trickiest. While I tend to avoid romance-based RP settings I know many others who chose to take part in it. Knowing that the player could be 15 is a good enough reason for me to avoid it. I wont even have one of my characters flirt with another character if I don't know for sure that the player is over 18.
If you're finiding yourself heading into an RP that you would feel uncomfortable if you found out the player was underage, or significantly older, it's essential that you find out the other person's age right away. There are plenty of in-character ways to get out of a sticky situation:
"My gold just came in from the Auction House!"
"I've just gotten a distress call from the Oracles! I'd better go!"
"Wait, you're a Scryer? This will never work. Get away from me!"
"I completely forgot to wash my hair today. I'd better go do that."
If someone asks you how old you are, just be honest. There are some people like my friend who feel uncomfortable playing with underage people. Don't take it personally. At the same time, a child's parents might not want their child playing with 30-year-olds in game. This is understandable! There are hundreds of other people on your server who would love to play with you. Just move on.
For guild leaders
If you have an age policy in your guild, stick with it! My friend was so disappointed to find out his guild wasn't sticking with the policy. If you're going to make exceptions, do it sparingly and for very good reason only. Inviting a 13-year-old because you really need a shaman is not a good reason. Inviting a 17-year-old because his best friend is in the guild might be legitimate.
Sometimes guilds change policy and that's okay, but always make sure to let your guild know beforehand and explain why the policy change is taking place.
For guild recruits
If age policy is really important to you, ask one of the guild leaders or officers how strict they are and what kind of exceptions they make.
Don't lie about your age to get into a guild. Officers can often tell--as someone who used to read tons of guild applications for a 21+ guild, I can tell you this is true. If you do slip through the cracks you might end up getting outed and embarrassed later on. I can understand why a particularly mature 16-year-old might want to join an adult only guild. However, there are guilds out there without age restrictions that value maturity.
On the telephone line, I am any height, I am any age I want to be. -Savage Garden
People lie about their age enough in real life, but online it's even more prolific because people can't actually see your wrinkles or acne to determine that you're a senior citizen or a teenager. As always, be careful what you tell or do with people on WoW because regardless of what they might tell you, there is no knowing for sure who they actually are.
Apologies for the 90s song references in this post.