Formulations containing plant extracts, in particular Astragalus extracts, and their use in inducing telomerase activity in cells, are described. Such compositions include pharmaceutical, including topical, and nutraceutical formulations. The methods and compositions are useful for treating diseases subject to treatment by an increase in telomerase activity in selected cells, such as, for example, HIV infection, various degenerative diseases, and acute or chronic skin ailments. They are also useful for enhancing replicative capacity of cells in culture, as in ex vivo cell therapy and proliferation of stem cells. Also described are cosmetic formulations of such extracts for conditioning the skin.