Recovery phrase: xxxxxxxxxxxxxx
When you posted your wallet mnemonic seed words like this, your wallet is accessible by many other people, and your fund can be stolen too.
Remove that part immediately.
I have an old Trust Wallet recovery phrase. I imported it and see 18 USDT balance but I'm confused about TRON network.
But when I try to withdraw, it says "Insufficient TRX for gas fees".
How much TRX do I need? Is this normal for TRON?
The information means you have USDT on TRON blockchain, and on that blockchain, TRX is the blockchain native currency which is used for on chain transaction fees.
This means to move TRX on TRON blockchain or any TRC20 tokens on TRON blockchain, you always need TRX for transaction fees. You must by small amount of TRX like about $5 to $10 and send it to that wallet address, for using TRX for on chain transaction fee of your USDT transaction.
Definition of tokens.After that, you must (remember MUST) move all fund in that wallet to a new wallet. Because the wallet should be assumed as compromised by your careless post with the recovery phrase initially.