Stem cell therapy as such is still not fully developed science. While the therapy is breakthrough, doctors say there is a great risk in the treatment itself. Our own cells can turn against us over time. It is also dependent on where the stem cells are taken for storage.
The process is not effective if the person is elderly as the ability to undergo the process itself is painstaking and the effectiveness is questionable. Our body evolves over time and the stem cells become irrelevant after specified time limit. There are many reasons to support why stem cells are not tried on older people as it is scientifically ineffective and risk prone.