The coin days requirement should be reserved for usage by user option when there is an ongoing attack, as otherwise new users wont be able to trade.
Allow me to correct you on this non-sequitor. The newness of a user of a decentralized exchange doesn't require that user's UXTO is newly acquired.
I was thinking of someone that just got their first BTC locally. wouldnt that be too young to be used? maybe i dont understand the intended coinage well enough.
If we assume that a lot of new users will be using the DE, they will be coming from the CE. And maybe they never had a local wallet, so they do a withdraw. patiently wait the confirms so it is in the wallet, then start a trade (after all they are doing this to use the DE) and then told "sorry you have to wait X amount of time since your dont have the right time of utxo"
I really want to avoid having what is potentially a mainstream real world case have such an error message to be expected
James