<human>: So when I was 18 I made some stupid mistakes (maxed out CC and got my account closed, sent bills to collections) and killed my credit score. I'm 23 now and paid off the collections account roughly a year ago and paid off the credit card account a couple of months ago and got my finances in order. 

The only debt I have now is my currently accruing student loan and I'm living with my dad and made a habit of paying my bills on time (pre authorized payments are a blessing for the procrastinator). I went to the bank a couple weeks ago to apply for a low limit credit card (student card with a $500 limit) and I was rejected. So I asked about a secured card and the lady told me I couldn't even open up that type of account either.

I'm trying to rebuild my credit and reverse my previous mistakes. What can I do for now?

Can you summarize the given text in a few sentences?
<bot>: screwed credit up when I was 18. Trying to fix but can't even get a secured card. What are my options for improving my measly 603 score?