Oil magnate and Texas’s adopted son T. Boone Pickens suffered a “Texas-sized fall” last week that brought him face-to-face with his deteriorating health.

The 89-year-old Pickens was hospitalized following the accident, but seemed collected when he penned a LinkedIn post on Thursday titled “Accepting (or Embracing) Mortality.” Pickens’s fall came after a series of strokes in December 2016—and though he has famously said that he will never retire, Pickens acknowledged in the piece that his body is betraying him, even if he is still “mentally strong”:

Many of those who face adversity like this at 89 choose to hide it. My life has always been an open book. Some chapters of my life have been great. Others not so much. Regardless, I’ve appreciated the resulting accolades and criticism as I faced different personal and professional challenges.

Just a year ago I felt immortal, wearing my age with pride, even joking about it. Last year I opened a speech with this: “The other day I turned 88 and realized my life was half over.” I refused to call my 2008 autobiography “Life in the Fourth Quarter” because, well, hell, I wasn’t in the fourth quarter. But things have changed for me since the strokes. I clearly am in the fourth quarter, and the clock is ticking and my health is in decline, much as it is with others in my stage of life.

Despite what he refers to as “the setback,” Pickens seems to be looking forward. “Now, don’t for a minute think I’m being morbid,” Pickens insisted in the post. “Truth is, when you’re in the oil business like I’ve been all my life, you drill your fair share of dry holes, but you never lose your optimism.”

Ultimately, Pickens ended the post by advising readers to soak in one of his many nuggets of wisdom. “I’m fond of ‘Booneisms,'” he wrote. “Number 15 on my list is this: ‘Don’t ever let age be an obstacle.’ And I won’t.”