You can buy it for yourself today, but at expensive micro lab quantities on Amazon. Alkahest and Tony Wyss-Coray are making a run at it as well. In the next 5 years who knows. But the research has to be funded and capital invested. And NIH-funded research is at historically low levels so investors are needed. Lets see how it plays out and hope for the best.
I know this is hard to believe, but the vitamin and supplement market is so massive that even some of the *retailers* in this business run public companies with market capitalizations over $1 BILLION USD. See for example Vitamin Shoppe, NYSE symbol VSI. There are many many manufacturers of supplements with valuations over $1 billion.
IF there is demand...and IF there is no regulation on supply...for one of these companies to invest $5M in startup costs to support a unique production process for GDF-11 would be *spit money*. Even if you make pessimistic estimates, assume 2% of 80M aging US citizens are willing to pay $300/year for GDF-11 supplementation, that is a $480 MILLION USD market. And that is the US alone. It's very easy to build a return on investment case to invest $5M when you are comparing it against an unregulated large market of that size.
Contrast that to a highly regulated pharmaceutical. Because of the FDA meddling, the $200M startup cost requires you to find a multi-billion dollar payoff to justify the huge risks and large number of likely failures. It's a totally different case.
If you want to make it, I'm 100% behind you but don't delude yourself. If I like what I see I'll help promote it, but I believe we still need more data. GDF11 isn't as effective as whole blood or plasma because other factors are working together. Once the proper cocktail is determined as I eluded to before several factors will be combined so as to give similar results to the parabiosis experiments. GDF11's scope is still impressive, but alone I don't see the hype as reality.