Early on in my pursuit of understanding the brains architecture and how one would go about emulating the brain in a computer, I kept running across statements to the effect that it was impossible - just too complex. So, having taken a course in embryology, I wondered if it might be possible to construct a brain by growing it and following the developmental stages. This led me to recognizing the decreasing potency of cells as they were reproduced and became more and more specialized. Something had to be controlling the production of specialized cell types at various stages. My imagination conjured up a method by which a template molecule crawled up the DNA helix opening the strands so that tRNA could transcribe stretches designed to produce the necessary structural proteins. This process would continue from the moment the template molecule encountered a start codon until a matching section hit the stop codon, then the cell would separate into two daughter cells. The mitotic process is known to shorten the telomeres with each cell division, thereby establishing a new starting point for the template molecule for the next cycle. The process moves the cell ever closer to becoming a specialized cell and would also control the population size of the particular cell type by virtue of the template molecules length.
Now comes an explanation for why the cells retain junk DNA. I don't know if this is true, but the junk DNA could be a logical means of establishing a counter mechanism. If genes were separated by stretches of junk DNA, they could correspond to how much protein should be produced during the cycle of reproduction. If this were true, then aging and death could be a byproduct of the mechanism for development and growth - telomeres get shorter and shorter until the cell can no longer reproduce. The cell, then, breaks down from natural ware and tear. The addition of more junk DNA by retroviruses over the generations could explain how humans have become larger over time. Thymus shrinking could be the result of cell deaths and related too earlier stages during the production of the thymus.
Part of the key to extending the life span of humans is wrapped up in lengthening those telomeres, but there's more to it than just that. The mitochondrial DNA also ages and die off. The medical wizards know that the telomeres can be rebuilt with telomerase for they see it happen all the time in cancer, so the mechanism does exist in the genome - probably engages during fetal production to offset the shortening of inherited DNA from the parents. You have to wonder if children born of very young parents would have longer life spans than those from older parents (?) I'll Google it and see if anyone has surveyed and published on it.
Ya know, so much research funding has become dependent upon government sources, there's a goods chance that funding research into longevity will drop to negligible levels. We hear so much rhetoric and fear mongering concerning global warming while the real threat is related to over population. The Population Bomb could explode during the life span of the next generation. Invest in Soylent Green!