My son has always done this and it doesn't seem to matter how many times we tell him to put all his feet on the floor he still does it. It's not so noticeable when he is wearing shoes but indoors it's very obvious.
My 7 year old does this too but his is sensory because he has ASD but this son is definitely not on the spectrum so wondering why else he does it and also concerned about any damage he might be doing?
Do you have any other concerns about him? How is his co-ordination, etc? I ask because tip-toe walking is very common in Dyspraxic children - but if you have no other issues then presumably it's just a bad habit. As to what you can do - hopefully he'll out-grow it but if constant nagging isn't working it may be worth talking to your GP for advice.
I've not noticed any clumsiness or coordination problems. My autistic son also had dyspraxia and he is very clumsy and spatially unaware but there's nothing obvious like that with this one. I think it is just a bad habit that he doesn't even realise he does!
My DD1 used to do this. She stopped eventually, but was 10 or 11 by then! She does have short Achilles' tendons, but GPs were never concerned about her. A friend of ours who's an orthopaedic surgeon had a look at her and sent her for biomechanics assessment. She had some exercises to do which helped a bit, but she still kind of flips her feet forward rather than the usual heel to toe strike. It's odd to watch, but doesn't seem to cause her any problems. I was worried about the effect on her knees and hips, but the ortho said it shouldn't be a problem - it's just a variation of normal. If it's worrying you, maybe you could ask for a similar assessment for your DS? DD was seen once she'd stopped toe walking.
Thinking about it more he often complains of pains in his legs but I've always said "growing pains" which it still could be but it could also be because of how he walks. Think I'll mention it to the doctor and see what he thinks at the very least.
I always used to walk on tip-toe when small. I am nearly 50. I now have very large calf muscles and am not that flexible. My son does it occasionally. I try to stop him. Constantly saying "Heel toe" as he walks. No idea why we do it.