Any interaction with SCP-XYZ is to be observed by one other on-site personnel
Remotely (through a one-way mirror or CCTV cameras) or face-to-face with the SCP and interviewer?
Based on the degree SCP-XYZ has aged since in Foundation custody from regular health assessments, it is believed to be at least over 3000 years old.
Personally, this broke my suspense of disbelief. Is this trait (supposed immortality) even needed for this SCP's narrative? If not, I don't see why it should have a place in this article. SCPs don't need to be ever-lasting.
SCP-XYZ is capable of recalling events that, as it describes, other have “forgotten.” This includes memories targeted by Foundation amnestics. Its recollection of memories, however, are not eidetic, as they seem subject to the same type of decay, bias, and rewriting as normal memories.
Huh? The wording here is rather oddly phrased. Given what you have written, it implies the "it does not need to eat" and "gaining others' memories" are not cause-and-effect. It feels as though it happens to gain others' memories and need not to eat as separate traits.
Instead, I would suggest this: "SCP-XYZ does not require food or water to survive, instead feeding on the memories of other individuals it has interacted with…"
On that note, does it feed on memory alone or what memory that a person has forgotten? If the latter, you might want to do more research on how memory works (since I feel the writing on the topic feels rather wonky and does not imply the level of knowledge in the topic that an in-universe Foundation researcher would have).
(due to the confusion caused and potential security breach by those who have taken amnestics, SCP-XYZ has been strongly discouraged from saying this).
Since I supposed that researchers who are dealing with this SCP would have read its SCP document, they would know the context of what it said (that it fed on their forgotten memories). Also, if letting the SCP feed on forgotten memories is a security threat, then the procedures would have attempted to account for it (such as "No personnel interacting with SCP-XYZ is to have a history of amnesia or amnestic treatment").
20lbs
Please use metric/SI units. The Foundation is posited as an international organisation, which follows the international standard of doing things (including measurements).