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[mrsshep77]

Have his eyes gone milky recently? Your temps seem ok and diamonds don't like too humid an enclosure. Does he have access to a large water bowl where he can soak himself? At his age shedding is a natural part of nature and he's not shedding he's not ready to shed and nature will take it's course. It seems your are doing everything you need to be so just don't worry and unless you notice the snake is unwell or seems stressed or isn't eating, then it'll happen when it happens. Our diamond goes off his food when he's going to shed and becomes very lethargic and anit-social.
If soaking isn't working the old skin may not be entirely ready to come off, so don't try peeling it off unnecessarily otherwise from what I've heard you can do damage to the scales.
Good Luck and I hope this helps