And I do indeed suspect they'll find some downside to this somewhere, likely in either cancer rates or metabolic issues.
As a researcher said the other day (I can't locate the link right now), "In the end, if heart disease doesn't get you, cancer will."
In experiments performed on mice, blood transfusions from young mice reversed age-related markers in older mice. The protein involved is identical in humans.
http://mic.com/articles/88851/harvard-scientists-may-have-just-unlocked-the-secret-to-staying-young-forever