I think an older beginner has to be realistic about what they will might achieve, depending on how old they are. MA are about coordination flexibility, balance, strength, stamina and tenaciousness and only one of those qualities is likely to improve with age without a great deal of effort and the neuroplasticity that younger people possess; learning a skill requires the rewiring of the brain as that skill is wired into our synapses and that plasticity reduces with age. I’m not suggesting an older beginner will be unable to be perfectly competent in the MAs but I doubt they’ll have that certain ‘something’ that makes them truly accomplished.
I had a private Japanese language teacher, the beautiful Ai sensei who happened to be a 5th Dan in Iai and she had beautiful technique. I asked her why Japanese exponents of Iai just seem better than us Westerners, their cutting in particular. She replied it was just repetition; they tended to start MA training as young children so had completed more reps at a young age than most Westerners do in their entire lives! When I used to go skiing, I’d see three year old German/French kids learning on the slopes and see 12 year old zipping down black runs effortlessly. Try learning the piano/guitar/violin as an adult. You’ll be OK but you won’t be Nicola Bernadetti
‘Youth’ is wasted on the young!