This was exactly the situation I was in 5 years ago with ds2.His birthday is January but he didn't walk until the following september,19 months ,I don't think I was so aware of it as ds1 was very advanced on speech so I just thought that it was ds1 that was advanced not ds2 who was behind.He was also a cherubic baby ,all curls and dimples and to be honest I carried on treating him as a baby.Anyway to cut a long story short we have had speech therapy HV appointments etc,ears tested and paed appointments because of a chronic constipation problem (fiinally solved by homeopath) I could go on but the general opinion was that he just had a non specific developmental delay,it's almost as if he stopped developing at 12 months nad then started again 9 months later.He is 7.5 now and and still more like 6.5.
He started at the fairly academic independent school that his brother stated at(I can't believe I did this too him adn even now feel hugely guilty) but it was a nightmare because he was more like 3.5 not 4.5,the school were lovely, they had known him since birth and could not have been more supportive but it was obviously not the school for him,so we moved him to a small less academic school with very good SEN support and he has blossonmed.Even manging to write joined up!
In retrospect and after a lot of reading on mumsnet and elsewhere I think that he is at least borderline dyspraxic,he eats neatly and can ride a bike with stabilisers and his speech really took off at about 6 years,the speech therapist said he had a large tongue which did not help him especially as his general co ordination and muscle tone is not good ,although strangely he kicks a ball more naturally than his elder brother,however he only learnt how to ride a scooter last year and his 2 year old younger brother can do this already.
I also think that some of it is just personality and one of his teachers who is in her fifties did say to me that 30 years ago he would have been classed a latedeveloper and nobody would have been worried as long as he got there in the end but now we have very rigid ideas of what is a normal spectrum development and what is not.A lot of his problems have been compounded by a lack of confidence in his abilities because he is so used to not being able to do as well as his peers,but with the schools support we are conquering this and at the moment I am loath to look for a for,a formal diagnosis but keen to let him progress at his pace and gain some confidence
Incidentally your description of your ds is identical to mine of ds2 at the same age,I would stress that we never had a problem with eye contact,it would also have been a perfect description of my own brother 30 years ago and this hasd kept me going,he has a Msc from Imperial College and runs his own business,it all came together for him when he was about 10.
I am racked with guilt daily that we did not pick up his problems earlier and always wondering if it is something that I did so you are a fantasic mum for raising it now,I just kept allowing myself to be erassured by people and saying"he's ffine ,don't worry" and bt dh who didn't want him labelled so don't allow yourself to be fobbed off and go with your instincts,I wish I had done ,even though things seem to be working out now.