The full journal article says "in vivo" not "in vitro". They have already successfully regenerated mice which are organisms biologically similar to humans.

Edit

I was wrong about this. The journal article does only talk about results obtained "in vitro" but mentions other studies that have successfully reversed cellular ageing "in vivo".

The ability of the Yamanaka factors to erase cellular identity raised a key question: is it possible to reverse cellular aging in vivo without causing uncontrolled cell growth and tumorigenesis? Initially, it didn’t seem so, as mice died within two days of expressing OSKM. But work by the Belmonte lab, our lab, and others have confirmed that it is possible to safely improve the function of tissues in vivo by pulsing OSKM expression [22, 23] or by continuously expressing only OSK, leaving out the oncogene c-MYC

So in this study the results were only in vitro but other studies have successfully reversed cellular ageing in vivo.