Biohacker Bryan Johnson has been looking to defy Father Time by aging as gracefully as a bottle of wine ... except now he's faced with biologically insurmountable odds.

Bryan sat down with TMZ's Charlie Neff ... he discusses his incurable autoimmune disease diagnosis -- which the longevity influencer revealed on social media last week -- but it's safe to say it hasn't wilted his spirit.

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Despite the sheer irony of a man who's whole brand is defying age suddenly coming down with an incurable disease -- Autoimmune Gastritis .-- Bryan's reaction to his diagnosis is "it's wonderous."

Bryan mocked the haters of his content who feel he's playing god by divulging in ways of preventing the physical toll of the passage of time ... urging them to come tell him "I told you so" at his funeral.

According to the longevity influencer ... this disease has been progressing unnoticed for the last decade or two ... and the result is he can no longer absorb iron, B-12, or other micronutrients which will inevitably lead to lack of nutrition and even to cancer.

If that sounds grim ... Bryan certainly doesn't think so! In fact, he says this diagnosis is only pushing him and his team to defy death by finding a cure!

Check out the full interview on YouTube where he also talks about whether he thinks its still possible to live to 160 years old and what his plans are for his body when he dies.