Hi there. You're doing the exact same thing I'm doing, but in reverse. I'm a mature student who messed up and did half a degree in the USA in a subject I no longer wish to study, and I decided to go from CA to the UK.
I will save my normal obligatory warning about how horrible Los Angeles is
The US does have a mature student equivalent, but as far as I know it tends to differ from university to university. Your best bet is to narrow down to a few you're interested in and contact them.
As far as credit transferring goes, I don't know FOR SURE but I don't think most schools will accept credit transfers. HOWEVER, if you got a 2yr qualification in the UK, you MIGHT (big might, I don't know for sure) be able to have them accept at least part of your credits under the General Education requirements for your degree.
Like I said though, that's really up to the individual uni.
Since we're both in similar situations, I'll tell you to do what I did - learn the ins and outs of the university admin system. Write to people in all the unis where you are thinking of applying and tell them, in detail, about your specific situation. Don't expect a lot of luck, namely with the transfer of credits - but you might get lucky if you work hard enough and make the right contacts
As far as the student loan, I can't help you there. FWIR, you need to have an independent source of funding to study in the US. Since you're thinking of going to CA, the prices are going to be phenominally high. There aren't any unis in the US that will give you money to study there outside of Harvard, Yale, etc, and you won't be eligible for US Federal Student Aid.
I know this all sounds discouraging, but I don't mean for it to be. If you really want this and you work hard, you have a chance. Sorry I wasn't more helpful, just telling you what I know.