You're 24 don't talk about your childhood other that you diagnosed yourself with ADHD as it seemed to fit everything that you were dealing with - its annoying and might make you seem like your just trying to get a script if you pull the 'when I was 12 story..' Getting a prescription for adderall (or any adhd medication for that matter) has stigma attached to it unfortunately - mainly because a lot of people divert it.
Realize that and just relax, if you need the medication - then you will get it - talk about the symptoms you have - a great way to get it is to say you feel if you were treated earlier in life you might be further along - talk about your inability to focus, prioritize tasks, and that your mind is always wandering. Say that this produces anxiety ( you want to be distressed that you have adhd - the purpose of medication is to relieve the symptoms and thus the subjective distress.) If no one was distressed about adhd we wouldn't have medication for it.
Go to a psychiatrist, preferably a younger one.. I am close to your age and my doc is 28. The older ones fall into two camps - those who prescribe it and those who wont. The younger ones who take cash will write it for you. Please don't divert it - as it actually fucks over the people who need it :/