Yeah, it works. I have three brothers. There are 2.5yrs between me and DB1, 7.5yrs for DB2, and 19yrs for DB3. We all get on and have lots in common, even DB3 who has the biggest gap.
I have DS who is almost 2yo and I'm 30wks with DD. I'm having a break after this one and will try again when she's around 12-18mo. By the time I get pregnant and carry the baby for nine months DS will be around 4/4.5 and DD will be 2/2.5 give or take a few months.
me and my sister were four yrs apart and so were her and my brother and we all hated each other. i got on with my brother because he was the youngest etc but not the closest sibling iyswim. i think i was about what we would be in to when we were very young not so much of a problem but there is a massive difference between a 10 yr old and a 14 they have almost nothing in common and yet the younger will still want to play with the older etc. having said that my eldest and middle are only 2 yrs apart then next child is 4 and when i have this one the gap will be five and they all get on pretty well.
I have this age gap between my children. DD1 is now 5.5 and so far it has worked well. I have had time with the baby whilst her sister is at school and the elder sister is very helpful and protective of her sibling. She did have a spell of playing up when the baby arrived but only with me, not with the baby. I suppose that's expected. I make sure we have some time together and it's been lovely taking her to school and collecting her whilst on maternity.
I don't know what the future will bring of course, but so far they play well together and I am hoping that, even if the teenage years are a bit distant, they will be there for each other when they are adults.
My sister and I were always very close growing up and she's 4.5 years older than me. Even in her teenage years, we still spent quite a lot of time together because we had interests in common. I really missed her when she moved away to study at 17. The time we were least close was probably when I was in my 20s as I felt that she struggled to relinquish the bossy older sister role. It has evened out a bit again now we're in our 30s.
DH's brothers are 5 years and 10 years older than him and he doesn't get on with them but that's more because of personality clashes rather than the age gap. He had been quite close to his brother who is 5 years older than him when he was a child and teenager but, again, his brother couldn't really cope when my DH got into his 20s and the 'hero worship' phase was over. So it seems the 4 or 5 year age gap works fine for kids and even teenagers but can be problematic later in life when the older sibling has to adjust to the younger sibling being a mature adult, not just the little sister/brother. .
DD will be 6 years 5 months old when this baby is born. I had wanted around 4 year age gap but it didnt happen so Im happy with what Ive got. DD will love the baby anyway. And I will get lots of time to spend with baby as she will be at school etc.