I got this from Askmen.com. I'd probably add my insights whenever I have the time. XD
There's a lot of downright stupid stuff society will give you a pass on while you're still in your 20s, but most of it ceases to be amusing and just gets depressing as you soldier on toward middle age. In a larger sense, though, approval is about achievement; we expect people to improve themselves as they age, so if you're working the same meaningless job and acting just as you did in college, then you're not improving much of anything. Thirty is a big milestone, and it's also a point at which people are going to start to wonder what you're doing with your life.
No.10 - Eat fast food
We're not arguing that you have to become a vegetarian here. You don't even need to spend a lot of time or consideration on preparing your meals. But a decent, healthy, inexpensive meal is not at all that difficult to throw together in, say, five minutes. There are plenty of recipes for healthier eating out there, and many are designed for people with no substantial kitchen and no motivation to cook. Regardless of how little effort you put into it, almost any reasonable meal you make is going to be far better for you than the cocktail of heart attacks and hypertension you're getting with fast food. I'm kinda guilty here until now and probably until the day I die. XD
No.9 - Drive recklessly
The Wikipedia list of famous people killed in traffic accidents has hundreds of entries. About a million people die from traffic collisions every year, and about 50 million more are injured. More than just a behavior for the young and foolhardy, driving like an idiot means ruining your (or someone else's) life. You’re too old to tailgate someone at 70 mph just because you don’t like the look he gave you. If you have trouble imagining the consequences, think about how it would feel if you woke up in a hospital with no legs. Uhm, I have no car so this won't be a problem for me. XD
No.8 - Play video games obsessively
Games are branching out to diverse consumers as best they can. The development of phone games, the explosion of small indie publishers and the amount Wii spent reaching out to non-gamers old and young is making gaming more prevalent. That part of the market is one thing, and nobody's going to look down on you for playing some iPhone game while you sit on the subway. But when you slouch in front of the computer for 48 hours because you're obligated to kill a specific number of orcs, something is amiss. You can't expect to make any real progress in life if your first priorities lie in a world that only exists on a server. The only video game I play is Mafia Wars from Facebook. Does that count? XD. Seriously, I haven't played any serious video games since 2000 and I guess I have moved-on from that phase.
No.7 - Live in a dorm room
Metaphorically, that is. By the time you're 30, it's expected that you've developed some sense of taste and style that's reflected in how you choose to live. If you're still surrounded by beer posters and five-dollar furniture, then people are going to infer a lot about your level of maturity from what they see (and it's probably a pretty accurate assumption). Make an effort to keep everything clean and to present yourself like an adult. I never lived in a dorm room and perhaps I never will.
No.6 - Get a tattoo
Before you get too defensive, note that we're not saying there's anything wrong with already having a tattoo. It's just that most regrettable tattoos -- whether they be an homage to a long-dead band or the pedestrian tribal design -- can be explained as the rash decision of a twenty-something. You're going to be hard-pressed to explain how body modification fit into your thoughtful, adult considerations if you get one after turning 30. I'm having thoughts on getting one for quite sometime now and I guess this isn't for me. XD
No.5 - Binge drink
Of course, nobody's arguing that you need to quit drinking entirely. There's nothing wrong with drinking in moderation, and in fact, you'd probably find yourself in some awkward professional situations if you were to decide not to drink at all. But there's a point at which regular, heavy consumption literally qualifies as a severe chronic illness, and if you haven't worried about that at all yet, hitting 30 is a good time to start thinking about it. Uhm, I've so sober since I got married and I kinda missed going on drinking sprees. XD
No.4 - Live paycheck-to-paycheck
Most wealthy men are wealthy because they were considerate enough to save or invest their money. Long-term wealth is something most of us really have to work at, even if that just means having the restraint to save something -- anything -- every month. If long-term wealth isn't motivating enough, consider all the unforeseen opportunities and emergencies that might require you to have some cash ready. Are you comfortable being totally unprepared for those? It’s time to start saving. Shoot! This one is a tough nut to crack. I guess I have to live within my means now.
No.3 - Work at a dead-end job
Your current job -- the thing you spend your time doing right now -- is how people see you, and it influences how they treat you. When you're defining yourself, either on a form or to another human being, this is one of the first things you'll be asked. Obviously you have plenty of time to figure out what you want to do with your life; you don't need to be an entrepreneurial firebrand straight out of college. But if you're cresting 30 and no dream job has fallen into your lap yet, maybe it's time to consider that you've waited long enough and that it's time to make some changes. I love my job right now but I need to move up the ladder ASAP.
No.2 - Be socially/politically clueless
In American demographics, the term "youth vote" literally means "18 to 29," so by at least one metric, hitting 30 places you cleanly out of the youth category and into the mainstream. The further you go professionally and the more you expand your social horizons, the more you'll be called upon to converse like an adult who actually understands the world. Your politics aren't the issue -- that's not what this is about. It's just that, after a point, you need to know when people are talking about a playwright or a country. I have no idea about this. XD
No.1 - Dress like a slob
Even more important than your job or your personality is how you dress. It’s one of the first things people are going to notice about you (and before you even speak to them, they'll already have partially made up their minds about who you are and what you're like). Just as with cooking like an adult, dressing like a man doesn't really take time, effort or even money. It only requires that you care about how you present yourself and to realize that more is expected of you now than 10 years ago. For me, as long as I look good, its all that matters regardless of what most people would say.