Understanding the Body's Natural Balance: A Look at Health Across Lifespans

Question
I had more of a general observation. It seems that when people are younger they change to prepare themselves for the longer term future. For example younger people have less complete immune systems and when they get sick it can be quite extreme, but once they get through any sickness they become so much stronger. Even during puberty a person's body seems to be at odds with itself while it finds a correct balance. I'm 30 and it feels like my body does now only what it needs to do to survive another day. Perhaps no more than a week in advance. Do you think the reason people age and their bodies break down is because there are fewer and fewer large trials to throw our balance off just enough to help us basically "redefine" ourselves as physical beings? It seems like when people get older they suffer fewer immunity type issues and they become "soft" so to speak that when they die it's likely something very small. I donated blood a few days ago, and I find even that slightest imbalance can make me feel full of energy and purpose and thriving to bring things back to the middle. I hardly was even thinking about who might benefit from the blood. I was in the hospital for my appendix before and was fed entirely by IV for 3 days, which although was weird and I had become hungry, I did feel much stronger. Do you think there is much merit to my theory, because I hate to think that I absolutely need to feel old now, and still have perhaps 50 years more to go?

Answer
interesting theory... there are other similar theories, but in general, aging is very complicated and one aspect has to do with the limited longevity of cells, ie their ability to reproduce ends over time.  Has to do with telomeres (ends of chromosomes) and there are many studies going in to how to modify that... but you are right in many respects with the immunity link.