If you created a Bitcoin address in greenaddress wallet of course that is a valid address, but the easiest way to check if a Bitcoin address is a valid one is to check it on blockchain.info, just copy the address and paste it on the search bar of the site, if the address is valid you will see the previous transaction, if not valid it won't show anything or error will be displayed. Another option is use the passphrases/private key and import it to other wallet that supports importing passphrase/private key, if you will have the access to it then that is a valid Bitcoin address, if you can't import it, it means that the passphrase is not legit.

Blockchain.info is the only place I use to verify whether an address is valid or not. Even if there hasn't be any transaction gone through is possible you will see zero value, meaning is valid. If there has been a transaction too,  you will see the previous and current balance.

A non-technical way to verify if the Btc wallet address is legit and valid will have been to send a very small fraction of bitcoin to it and out of it but the current hike in transaction fees makes that method not usable.

Meanwhile, the wallet provider should indicate when an address that was inputted is incorrect or invalid. All the bitcoin wallets I have used both web and cold storage does that for me.

What is the legit BTC wallet?

I have not seen any reports from bitcoins users that they are using fake bitcoins wallet. But, my advise to you is choose the best and legit bitcoins wallet that are the most trusted by the users.

Look man, just think about it. What would be the benefits of making a fake bitcoin wallet address? I just don't think that any troll would waste so much time making apps and buying dpmains just to make a fake waller. Just doesn't make sense. But hey, i understand. And i don't think that there is anything wrong with being sure. So if you really wanna know, just go to blockchain.info and paste the address. If it isn't an error, then it is legit.

Just one of them is blockchain.info, you just need to put your Bitcoin wallet address into any BTC blockchain browser for querying, and if the information matches, it's natural to prove everything

That cannot be right, suppose someone makes a mistake or a typo in the address, how to know if its right or now? Is there a way to verify or validate an address before sending out coins? There must be.

why shouldn't it be legit since its your own....