To be honest, I'm not very up to date on cloning. I could take a look a it. However, here in cancer research we are very familiar with telomorase running amok, where the ends never terminally shorten. AFAIK one of Dolly's suspected problems was that the telomeres had already substantially shortened, and they either picked up shortening more at that point, or the telemorase wasn't making up for what had already been lost. But all cells can express telomerase with the right cues, and a number of adult cells do. TBH I'd bet that Dolly had a number of other problems due to a previous life that simple nucleic transfer didn't reverse. Biology is crazy dirty. There rarely seems to be one problem or one solution. Typically the best you can do is to get the body to start doing the thing that you want it to, and let it go with broad guidance. My guess is we will figure out some slick ways to add a few decades, and then a few more, then a few more...