I had an old lady attending taekwondo were I went. She did about as well as anyone of us (except for the really fit) and she thought it was great fun. so I guess my answer to your question is "no".

Martial arts is not a work out many martial arts have been turned into exersice and sports but they are not true mortial arts. sure martial arts keeps you fit but that is not its primary purpose. there are martial arts for everyone.

There are so many martial arts with such vast differences, that a general question such as this can not be answered with a general yes or no. It sort of depends on the specific martial art. Some martial arts are strenuous sports that absolutely require a fit athlete in good health, while other martial arts teach health science and fitness so the young, the old, the weak, the sick, and the women & children can all learn to live a healthy life as well as learn some self defense. Look at the difference in training methods between Muay Thai Kick Boxing and Tai Chi Chuan ... an eighty year old new student with a bad hip and fragile bones will have difficulty even surviving the rigorous bone pounding of Muay Thai, but will be partially healed, revitalized, and have bones strengthened from the "Chi Kung" portion of the Tai Chi Chuan training. From my personal point of view, the mix of martial arts that I have studied, and now teach, are for anyone from age 2 and up, in any state of health (other than highly contageous infectious diseases), including wheelchairs and limb amputations. Personal limits due to health and handicaps will certainly influence the student's progression through the martial art, but will not stop it from at least getting started ... so long as the student can pass the tests, they can proceed to the next set of lessons. The young and healthy will progress with more speed, and it will always be much better to start the very first lesson at the youngest age possible, but even the old, sick, or handicapped can at least learn a little something, even if they never reach master or grand master. __________ ... I should add this ... My first Kung Fu instructor was 97 years old when I first met him ... yet he was STILL taking lessons from his father, the grand master !!! These guys looked like 50 to 55 year old brothers, and were in amazing health ... they both ran 10 kms. per day, every day, rain or shine or even blizzards ... they both died in a car accident when the propane tank in the taxi they were in exploded when the cab was hit by a truck ... I only had the chance to study with them for 6 weeks, then I began to train with "Olaf Simon" (another old guy) at his "Temple Kung Fu" Buddhist retreat in Christina Lake, Brittish Columbia (where I met my current Ninjitsu grande master while she was touring the world and adding some Chinese Kung Fu to her family's Japanese Ninjitsu style). ... another one of my grande master instructors was an old Tibetan woman ... she was having her 80th birthday and wanted a big party, a guy I barely knew had only been her student for a few weeks when he told me she had asked all of her students to invite their friends and families to the Vin Tsun school where I met her. I was amazed by her demonstrations, and I signed up and paid for three years in advance.

MA are certainly easier for those in their prime. But you never know until you try. With regards to age, it's not necessarily a limiting factor, and here's a great example: There was an historical figure, a French nobleman, Enguerrand de Coucy VII, who fought in the front lines at the Battle of Nicopolis on foot, hand to hand, laying waste to his opponents left and right, in full armour minus his helmet, which had come off. All this is fairly normal, except fot the fact the man was in his 60's. So certainly those of advanced age can be fearsome combatants. :)

I think wheelchair karate would be entertaining to watch.

tai chi is fantastic for the aging and weaker, and it can compete with the fit, depends on whos fighting of course but with some (ok lots) hand control training and practice you can make short work of most fighters

No. Traditional martial arts are for everyone. Great exercise for all, but don't dellude yourself into thinking that TMA will help you in a real fight. TMA's are practically usless in a real fight.