There are all sorts of opiate addicts who make it to old age, it's just not all that common for IV drug users in general. Presuming that you can get a consistent supply of good quality drugs, so you know what you're taking and not accidentally ODing from stuff that has fentanyl in it or is way stronger than you're used to, opiates actually are some of the least toxic drugs there are. You aren't damaging yourself by taking, not in a toxicity sort of way anyway (unless you OD of course, but ODing is avoidable if you're not rolling the dice with sketchy supply that might be fentanyl, or super pure when you're used to stuff that's weak).
It is true that a lot of opiate addicts die young, but it's mostly due to using drugs that are contaminated or of wildly varying strength, and the issues that come with a life of crime and/or homelessness, which, sadly, a lot of addicts face (but is not the drug's fault, it's the fault of the way we have set up society to punish addicts).