I am thinking once you have an account set up you can download tickets as often as you like but I know pensioner passengers who don't use the internet so they will suffer from technology discrimination especially if the download is paperless and is sent to a smart phone for scanning.
Once approved, you will receive an email confirming your concession account details, which will allow you to download free DART tickets.
Please note, you must carry your proof of ID when travelling on the Luton DART.