https://bitcoin.org/en/version-history it was something before 0.3 and since the compressed keys were introduced in 0.6 IIRC, your keys must be uncompressed. meaning in WIF (Wallet Import Format) they should start with 5 (5H, 5J, 5K). this is Base58 which are alphanumeric characters excluding 0OIl [1]

if it contains +, =, / then it is base64 [2]

if it contains numbers from 0 to 9 and letters from A to F then it is base 16 or hexadecimal [3]

you can use each of these above 3 in https://www.bitaddress.org last tab called "Wallet Details" to get your private key, pubkey and address.
if it is not one of these (unless i forgot something) it probably is either not a private key or it is encrypted and you need a password.

[1] https://en.bitcoin.it/wiki/Base58Check_encoding
[2] https://en.wikipedia.org/wiki/Base64
[3] https://en.wikipedia.org/wiki/Hexadecimal