I've studied claimants to mediumship for several decades. I myself have had the experience of deep-trance mediumship, psychometry and may have at one time been a PK agent. In my case, things tended to quiet down as I aged. From my research however, I find that this is more of a societal than chronological. In other words, could go either way. I know some highly talented mediums who are well past 40, 50 and even 70. One of this country's leading 'psychic detectives' (geez I hate that term) is past 70 and still going strong and doing well at her craft. On the other hand, I actually witnessed the decline of a physical medium I worked with many decades ago.
In all cases, these were documented, tested and legitimate mediums.
Hope this insight is helpful.
