5 year old all of a sudden taking ages to go asleep

Hi all. My 5 1/2 year old used to always be asleep by 7.30/7.45. this year we stretched that to 8/8.30 as he's getting that bit older. He'd always go through til 7 am.

For the last month or so he has started taking ages to go asleep. It could be 10/10.30 most nights before he finally goes off resulting in a very tired grumpy boy the next day. He is up messing at silly things....looking out window, taking things off wardrobes and in & out of bed.

I know they can reduce sleep normally from age 6 but literally a 2 hour sleep drop overnight seems a bit much especially when he so tired every day...he obviously still needs the sleep. I've talked to him & he insisting nothing wrong or bothering him to stop him sleeping. Any thoughts?