5 month old has a 5-6 hour wake window in the morning?!

[TeaAndMuffins]

So my 5 month old DS (second child) usually wakes up at about 6 or 7am, after which he categorically refuses to nap until 11am or even later. It's now 12.30pm and every hour since about 9am I've been trying to get him to nap in the usual ways that he is comfortable with. But he simply won't fall asleep. He is wide awake, alert and content, not showing signs of tiredness.
When he does this, he often has a very long nap when he eventually does fall asleep.
Has anyone else experienced a 5 month old who dropped their morning nap?
I can't find anything online about babies dropping it this early. I've read three different books on baby routines and they all insist on a morning nap until much older than he currently is.

At that age or slightly older, mine wouldn't nap but also was really unhappy with it - I did a lot of emergency long walks to get a nap in on the move. Baby magically grew into better day time naps at 7 months, nothing I tried before then made any difference and it was really stressful trying to look after a tired but wired baby :/

If he’s happy and content, I’d roll with it!

How is he sleeping at night? If he's doing well overnight for his age, I wouldn't worry about it. And if he's not getting upset. Otherwise I found the huckleberry schedules handy to follow. If you havent already, try rocking a pram with snoozeshade over?

Just remembered my ds having a strange nap pattern at that age - maybe 4 m regression related? In his case he'd just catnap throughout the day for 45 mins max so I don't know which is better really!

Neither of mine got the 'short first wake window' memo, so the morning nap definitely tended towards 11am or so. They were also both transitioning to 2 naps by 5 months, although I think a well-timed walk could still push them into three at that age (at least some days!).