but they didn't have all the different wallets and things they do now. so i guess it was harder to create your own wallet/address.
If it was hard to create your own wallet or key pairs from scratch, then it was probably even harder to find software which would let you import a raw private key to access coins you had supposedly bought.
no one should be needing to buy bitcoin from someone else using paypal these days though. since they can just buy it from paypal directly.
I would suggest you just shouldn't use PayPal at all, since they introduced a clause in their Terms
which allows them to fine you thousands of dollars if you say things online that they don't like.
Perhaps the format of the key is not Base58. The knowledge of wallet creation may not have been widespread in 2010, so methods for generating private keys may differ, You should try to decode your key with another format ex Base64, Base62
A possibility, although a raw private key encoded in these systems would be 44 characters, rather than the 51 OP has.