It’s a screening number. It’s not supposed to be “trustworthy” because it doesn’t mean anything other than as an arbitrary point for grouping individuals into categories that can be used to estimate risks and make generalized decisions.

As a thought experiment, consider another commonly used screening number, that breast cancer screening should become routine at age 40. Does that mean breast cancer doesn’t happen to women below age 40? Of course not. Does it mean breast cancer will always happen eventually above age 40? Also of course not. What does it mean? Basically nothing. There is nothing magic or medically significant about being 40 years old specifically. It’s just that we decide that’s a good approximation of the time when the benefits start to outweigh the costs for most people.

For an individual it’s a pointless number that is completely erased by a massive number of individual risk factors and situational factors. You are an individual. It does not apply to you.

For large populations, it’s a decent generalization. For people working with large populations, it can be a very useful measurement. But it’s not really supported to be anything more than that, and it’s not particularly useful to apply to you individually. We do of course frequently apply it individually, including many doctors (usually following the direction of insurance companies who DO care about large populations and DON’T care about you as an individual), but that’s not really particularly justifiable, that’s just a reflection of how our health care system works (or doesn’t).