The bull market "supercycle" for stocks and bonds is approaching an end, as the unconventional monetary policies that have bolstered asset prices since the financial crisis are running out, widely followed investor Bill Gross said on Monday.

The attempt by global central banks to cure a debt crisis with more debt doesn't have much further to run, which will end a rally that's lasted three and a half decades, Gross said in an investment outlook for Janus Capital Group Inc..

"Credit based oxygen is running out," Gross wrote in the outlook titled, "A Sense of an Ending," in which he compared the final stages of the financial market cycle with his own mortality.

Gross, who turned 71 in April, wrote: "A 70-year-old reads the obituaries with a self-awareness, as opposed to an item of interest. Some point out that this heightened intensity should make the moment all the more precious and therein lies the challenge: Make it so; make it precious; savor what you have done – family, career, giving back – the 'accumulation' that (British author) Julian Barnes speaks to."

Gross, manager of the $1.5 billion Janus Global Unconstrained Bond Fund, has made similar warnings on stocks and bonds before and acknowledged they've come too early.

In May 2013, Gross, who at the time was manager of the Pimco Total Return Fund, the world's largest bond fund, jolted Wall Street participants on social media with a Twitter post saying: "The secular 30-yr bull market in bonds likely ended 4/29/2013."

On Monday, Gross said successful managers who are neither permanently optimistic or pessimistic on the market have spoken to a "sense of an ending" as well.