I’ve got an old mandolin that my aunt kept in her attic for 40 years. Will it do?

It could of course be a fantastic instrument, and in wonderful condition. However, all that glitters is not gold, and it is also quite possibly

a) knocked out on the cheap for the Italian tourist trade, and

b) badly warped !

Even the quality turns out to disappoint, it might give you a start, and if you decide you want to stick at it and develop your mandolin playing, then members of the group will be very happy to advise you on where to find a decent instrument without breaking the bank. You may even find someone has an instrument for sale from time to time.