Follow the advice given in the replies above.
I started at age 68 with no musical experience at all. I bought a C/G Rochelle 30 button anglo off e-bay for a very good price. Got disillusioned after a month and then bought a Honer G/D melodeon which I got on very well with and still do, Morris tunes.
Picked up the concertina again about a year ago and haven't looked back. The melodeon and concertina go very well together.
I practise every day, sometimes for odd moments, doodling the buttons to find out which buttons made what sounds, but always at least half an hour practising a few bars of one or two tunes; Very slowly until muscle memory took over and I could hit the right buttons and pull or push correctly every time for at least three run throughs, then tried speeding up. Always, always, slow enough to make sure all notes are correctly played then the speed comes naturally.
I have started to read simple musical scores as well but the best thing ever is Utube.
It has come to my mind recently to look for a replacement for the Rochelle. A move up market to an instrument with concertina reeds is my aim, although finance may be a problem as the wife wants the bedroom redone completely. I will get there.
As mentioned, I play for my local Morris team at Wickham in Hampshire and take both instruments with me, the melodeon for dancing outside and the concertina for the session in the pub afterwards.
Never too old, never too broke, never too dim.
Al