Yes. You do not have to be married (although of course you can be), or be different genders from each other (again of course you can be), or be subject to any other random requirements - if you want a joint savings plan, you can have a joint savings plan, as long as you’re both human, both at least 18 years old, and both in agreement that you want a joint savings plan.
You will both have an online login to be able to view and manage your joint savings account, and you can use a credit or debit card in either name to fund it (and change the card as often as you like if you want to take turns paying in etc. If you have any questions about joint savings plans which you would like answered before you start, just send us a message.