If someone has made a claim that they have life experience and their opinion, that is an observation, so its significance as at least outside-view evidence can still be interpreted in Bayesian terms. That means there is still analyzable evidence on the table, so the conversation doesn't have to halt: you can quote their claim as an observation, and argue about its interpretation as evidence. "So then, what are the odds that people with your claimed amount of life experience would have your opinion if that opinion were true, versus if that opinion were false? Are there other things that might cause people with your claimed amount of life experience to have your opinion without its still being true?"