1) Your life begins in your twenties.
This one seems like an obvious fallacy. First of all, what exactly are we measuring here? If anything begins in your 20s its probably liver poisoning or debt. On a more serious note, I think that everyone suffers from this misconception at some point (usually our 20s). And suffer is the right word. I'm not long out of my 20s (T-minus 10 days until I'm 31), but it's been kind of fun to look back at my 20s and realize it was easily full of the most fumbling, frustrating, and fizzling moments of my life. Your 20s are all about trying to get your bearings, and the ship is always rocking. My 30s so far have been about finally having my sea legs under me.
2) You'll never be as thin as you are in your 20s.
Lies. All lies. I know many people gain weight the older they get, and that metabolism slowing down thing is no joke, but, at 31, I'm the fittest (and thinnest) I've ever been. To be fair (or unfair as it was), I grew up chunky, chubby, or whatever other word you might want to use for it. By the time I was 21, I was morbidly obese. Despite what some might think, it had nothing to do with diet and exercise. I spent my entire life up to that point focusing on just that. Then, miracle of miracles, I was blessed with the ability to have lap-band surgery. And that's all she wrote. The point here is that in my 20s I grabbed my chance at health and I ran with it. I've never once regretted it and every year I get older takes me closer and closer to being even more fit and healthy. I went from being over 300lbs to running to half-marathons. In that order. You do the math.
3) Your 20s are when you find yourself.
I can't 100% disagree with this, but I would alter it a little. I would say your 20s are when you run around trying to find yourself. I'm not sure all of us (or maybe any of us) quite catch ourselves. Your 20s are when you try out all kinds of personalities, beliefs, interests, potential mates, and even food. It's been in my 30s that I've really hit my groove. My 30s have been the point in my life that have synthesized all that I found out about myself in my 20s.
4) If you don't get married in your 20s, you never will.
Pfffffft. Just pffffffft I say. I can't even count the examples of how this is wrong. One of the great things about loving Asian culture (and having lived there) is that there are so many great "role models" for a woman in her 30s (or 40s…or 50s) finding love and starting a family. The truth is I'm really glad I didn't get married in my twenties. Don't get me wrong--I think there are a lot of people who are happily married in their 20s. I'm sure that if I had met the right person, I wouldn't have even questioned the choice. But I'm glad I didn't. The things I went through, had to experience, and the experiences I was able to have…I'm not sure I would have been on that same path. My life would look so different. Though I suppose you could say the same about almost anything.
5) You have to know what you want in life before your 20s are over.
I heard this about college in my teens. It was a crock then, too. Sure, there are advantages to knowing what you want as soon as possible, but knowing what you want is not always an easy answer to have. Sometimes you have try some things out before they stick. I don't see my 20s as a waste. Not at all. But I did do a lot of "testing." In my 20s I had every job from a barista to a high school teacher in a foreign country to an on-again, off-again university writing instructor. Oh yeah, and I dabbled in writing. Never once in my 20s did I ever think that writing or publishing was a real possibility. Then I realized that it was more of a possibility for me than any other job I had tried. So…in the words of Gus Portokalos…there you go.