Lumina is currently available to US residents aged 21 and over. You can apply on mobile or desktop; the process is the same either way.
If you're not sure whether you're eligible, the quickest way to check is to start the application — you'll know within minutes. Have your details ready first: What you'll need to open an account.
Your account itself is carried at Interactive Brokers rather than at Lumina, which is why some steps happen on their side: Why your account is held at Interactive Brokers.