Every other athletic program in the world, including other Japanese gendai budo, use some form of strength and conditioning to prevent and rehabilitate injury, prolong active years, and create people who are more useful in general. People hoping to maximize their years in Aikido may benefit similarly.
While I believe that all martial arts should promote and encourage their members to remain fit, strong and healthy my experience of combat sports and my observations of others is that they are at more risk of injury. When I did Judo I suffered torn ligaments in my knee and hematomas on my shins. A friend of mine who is now doing Judo has broken his toes and his radius in his arm. While all these injuries heal and we can carry on training, I have found my school of aiki-jujutsu to be more conducive to training as I have not (thankfully) suffered any serious injuries yet. Yes I come away with bruises sometimes and sore wrists if it has been a particularly rigorous night of training (usually tanto waza) or a heavy focus on Nidan (nikkyo), I've also been punched for real a few times either by not moving quick enough or my partner not pulling their atemi; however nothing that has kept me off the mat. Continuity in training is very important in my opinion.
I desire to train for life, however, that is a big commitment and life changes in all sorts of ways. Take my current training for example. I received my ikkyu rank earlier this month meaning that I am now at the highest level of kyu grade before I go for my dan grade. I am one grade away from my black belt but I am emigrating to Japan before I can sit it! In the bigger picture this doesn't bother me - after all it's not all about the colour of your belt but your attitude to training - nevertheless I will have to begin all over again in Japan at white belt as I want to transition to Aikido. But who knows whether I will be with the same club/area long enough to grade to black when I'm in Japan? Who knows whether I will be able to commit to weekly training when I'm married or when I eventually have a family and who knows what my financial situation will be like several years from now? There are so many variables. I look at my senseis and shihans and admire them for the decades worth of training they have accomplished and long to imitate their dedication, but I can't make any promises to myself because I can't predict my situation in 10, 15 or 20 years from now. All I can do is carry on training as often as I can, when I can and enjoy my training, because if we stop enjoying our training we are less likely to continue with it.