In response to mnm464:
I was a vegetarian twice: once in my early 20s, and now. Below are my stories of a) how to do it wrong and b) how to do it right. I offer them in hopes that they can offer some insight into your own decisions. As others have said, however, at the end of the day we are just so many strangers on the Internet, and your best sources of information lie closer to home.
How to do it wrong: I was a junk food vegetarian in my 20s. I rarely cooked, ate out a lot, and generally didn't make food a top priority. When I became a vegetarian, I mostly substituted cheese for meat and probably ate a higher-fat, higher calorie diet as a result. I gained weight, and didn't feel great. I felt much better once I started eating meat again.
Almost fifteen years later, I tried again and it's now a fundamental part of my lifestyle. Though I'm certainly not an Olympic athlete, I do enjoy an active lifestyle with hobbies such as cycling, rock climbing, and hiking. Here are some things that made a huge difference the second time around:
1) I learned to cook. I really think that cooking is essential to eating better, period, whether you choose to follow a Paleo, vegan, Mediterranean, or any other diet. A great place for vegetarians to start is Mark Bittman's How To Cook Everything Vegetarian. That's been my bible. Rather than just give recipes, he explains what the various ingredients are, how to make substitutions, and how to improvise. I cannot recommend this book highly enough. Yes, cooking is a time commitment, but it doesn't need to be an exorbitant time commitment. I think that vegetarian meals can take longer to prepare on average than meat-centered meals, but it's easier to prepare large quantities and stockpile them for later. So being vegetarian isn't just about cooking vegetarian - it's about finding a routine that works for your lifestyle (for example, making a giant pot of lentil soup one day, that you can eat for the rest of the week).
2) I had vegan friends who introduced me to new ways of serving up plant-based protein sources such as tofu, tempeh, seitan, legumes, seaweed, nuts, seeds, and grains. Just as I believe you can't be a healthy vegetarian without learning how to cook for yourself, I also believe you can't be a healthy vegetarian while also being a picky eater. The right way to become a vegetarian is to increase the variety in your diet (by discovering new foods), rather than decreasing it (by eliminating meat, but replacing the meat with equally familiar but potentially less healthy foods such as cheese).
3) I dated (and later married) a fellow vegetarian. This isn't a requirement, as I know plenty of vegetarians married to non-vegetarians. But it does help a lot to have allies. When you say that "my dad says you can get all but one crucial amino acid from other supplements," this worries me because, well, your dad doesn't know what he's talking about. I suspect that he's conflating a longstanding myth (that vegetarians need to worry about "combining" amino acid sources to get "complete" proteins), and a very important fact (that vegans CANNOT get reliably get vitamin B12 through a plant-based diet, and MUST find a way to take vitamin B12 supplements in order to remain healthy). The important question here is, is your dad open to being educated? Are the people in your life willing to eat a few vegetarian meals with you, and help you explore vegetarian cooking and vegetarian nutrition? If they are, your road will be a lot easier. If they aren't, you'll need to educate them while educating yourself, which isn't impossible, but it's certainly more of an uphill battle.
4) I learned enough about the science in order to ignore the science. Let me explain this one. I think there is a HUGE amount of misinformation out there about how to eat vegetarian and maintain an active lifestyle. There's science, and there's pseudoscience. I can't help you separate fact from fiction, but I can advise you to read everything you can, listen to your body, and use common sense. Eventually, you'll hit a point where you can plan meals based on instinct and taste rather than bean-counting macronutrients (percentage of diet from fat, carbs, and protein) and micronutrients (making sure you get enough vitamin B12, vitamin D, calcium, and iron). The science is important, but being able to maintain a lifestyle without going insane means that you eventually learn how to plan a week's worth of meals without having to count calories, measure out protein, or sum up your vitamin intake. Trust your doctors, but also trust your own body. Also realize that every person's body chemistry is different. If eating vegetarian just doesn't work for you, then perhaps the best dietary choice is to make an effort to find sustainably and humanely raised meat and seafood. This also requires research, but it's research that's well worth undertaking.
In the end, I think it's very much an American myth that we can eat mindlessly and not suffer the consequences. I personally believe that there are many different ways to eat mindfully, and no one way is the right way. My way works for me, and it also works for my husband. Best wishes, mnm464, as you find your own way.
And just to add to the list of high-level athletes who don't eat meat: Rock climber Steph Davis maintains a great blog, and she talks quite a bit about her choice to be a vegan. She has some great recipes as well.
http://www.highinfatuation.com/
I completely understand why some would choose be vegetarian or even vegan. Good for them, but don't be preachy about it. As for me, I love meat but if I had to give it up, I'd become a pescetarian since I can't live without seafood.
I will probably always eat meat but with your help I think I will be reducing it even more. I am a creature of habit and have really learned over the last few years how to curb the appetite for bad foods and have slowly nearly removed them. Thank you for the tips. 
