Sorry I too am late to this discussion which I just came across today. With no previous Martial Arts experience I took up Aikido at the age of 50. Having injured my knee and told to stop running I was looking for something that was 'Mind, Body and Spirit' that I could do. Despite this limitation I gained my Shodan 1st-Dan Black Belt after 6 years and as I am, despite my increasing years, still getting better, I am looking to try for my 2nd Dan soon.
What I would say to any beginner in their maturing years is to give it a try, persevere and just enjoy it. If you persevere with your training and practice, and continue to enjoy it, you will keep getting better, and who knows where that journey will take you!