I'm 22. I'm successful according to my own standards. Never developed a serious addiction but was a heavy, heavy pot smoker until I gave it up for good (I hope) less than a year ago. I never was formally educated, dropped out of high school with two course credits needed to graduate and got them later (well, halfway through the last one now). But I'm alright. I make enough money to survive and stay very happy. I live in the country, live off of farming, people think I am okay for the most part and I spend most of my spare time working as an environmental activist, or making art. I don't use drugs barely at all anymore, but I've used all sorts of drugs, including amphetamines, MDMA, psychedelics, cannabis and opiates. The only thing that has ever been an excessively negative influence on my life was cannabis, and it was the only drug I ever developed a habit of.
Were psychedelic drugs a mistake? No, but that's relative to my life. I've had some pretty strange circumstances in my life, including a very strong and accepting family presence, and a wierd cultural background. By a lot of peoples' standards, I'm probably just a wierd hippie. By my own standards and my family's standards I'm doing just fine, even though I'm not rich and without any real formal education. And I don't use drugs anymore, for the most part. Although I could see myself eating some mushrooms or cactus sometime not so soon, I really have taken enough drugs, psychedelic or otherwise and feel that I got enough of it out of my system at a young age because I was allowed to without taboos or shame around it. At the same time, I did a lot of retarded shit that almost made me dead when I was younger and stupider, and I wouldn't like to see people do the same.
Really it's all relative to your background, your personality, and your life, and I don't expect anybody to have had as peculiar an upbringing and life as I have.