No.

No not over the internet. Was there anything in writing.

Lack of capacity is a defense to a contract, but it is nearly impossible to prove. How did you lack capacity?

You'd probably have to take it to court and/or have some kind of competency hearing to prove that the person signing the contract was not legally responsible because they were a minor, mentally ill, something to that effect. It would most likely be expensive and extremely difficult.

I don't think so. I would be hard to prove though. I've only had one business law class so I'm not 100% sure.

It may be possible to argue on the grounds that there was no 'meeting of the minds' - i.e. you and eBay/PayPal never actually agreed, since you thought they meant something entirely different - but on the other hand I think courts would feel eBay/PayPal had a reasonably founded assumption that you understood what you were reading (otherwise, the argument goes, why did you agree without referring it to somebody who *did* understand it?)   Incapacity to contract would require quite significant impairment on your part, and (given that you seem articulate enough) be unlikely to exist to the necessary standard.   If it wasn't a case of 'incapacity' but merely 'exploitation of low capacity' it might be void for unconscionability, but you would need to show that the other party both knew you were 'weak' and explicitly exploited this 'weakness', which wouldn't be the case with a standard-form contract that is handed to anyone and everyone requesting a particular service.   'Would not have agreed' in relation to an unread contract can sometimes work if it there are 'nonintuitive' terms in the contract, that is ones which no person would reasonably expect to be there, though I can only think of one case in which this has happened off the top of my head, and it's Canadian: eBay/PayPal contracts are almost certainly administered under US law so this probably won't help at all.