It helps to think about the basics when talking about telomere length and cell behavior.<p>1) Telomeres shorten with each cell division in ordinary somatic cells. When they get too short, cells self-destruct or stop dividing. So average telomere length in tissue is a function of cell division rates.<p>2) Stem cells support their associated tissue type by providing new cells with long telomeres. Thus average telomere length is also a function of cell replacement rates.<p>3) Average telomere length is at present usually measured in white blood cells. The rates of division and replacement here are tied in to many factors, including general health, autoimmunity, infection, state of the thymus, and so on and so forth. It would probably be better to use another tissue, such as skin, but that isn't the way things worked out in practice.<p>So telomere length is far removed from first causes in aging - it is largely a marker, largely of stem cell function in most tissues, but in immune cells with their varying rates of division according to circumstances, also a marker of all sorts of other unrelated or partly related things.<p>If telomere length is globally extended, you have cells that can divide more often without the need for stem cell support, and you also have more energetic stem cells. But those cells dividing more often are more damaged on average. This may or may not be important enough to do bad things such as raise cancer risk significantly in our species: more data needed.