I did a lot of research. Put the property minrelaytxfee=0.00000000
in your Node config and as soon as someone post a Transaction with such a fee, and there are nodes that allow this fee, your node will hold it in the mempool. Old transactions in the mempool are not synced between nodes. My Node just saves transaction to a file and reloads them. That is why it was looking like the mempool synced. It only syncs the blockchain, not the mempool.