1. Is there any value in "old bitcoins" compared to new ones?
For example, bitcoins that have been on wallet.dat since 2012 have a higher value than bitcoins since 2024?
Bitcoin is still bitcoin no matter the year it has been mined and kept in a wallet, it will make no change and can still be used for the same purpose and still maintain same value as the current price it’s been traded in.
2. I am also interested in if you transfer bitcoins 2012 year to another wallet, and the change returns to the old one, will they both become bitcoins in 2024?
Bitcoin is bitcoin OP, and the wallet it has been transferred to does not matter as long as it can receive bitcoin. Bitcoin is not physical fiat that you can see changes or can differentiate them when you see the year written on it to be printed.