My brother turned 15 two days before I was born. It was awesome having an older brother like this. He went off to Vietnam when I was in elementary school so that was scary but he came home and has been an amazing big brother my whole life.
My sister was 11 1/2 when I was born. She is my rock and someone I can go to about lots of things.
Although....she was born in the 40's and I was born in the very very very late 50's we were born into different generations. She was raised to be a perfect housewife and homemaker. I was born into a time when women were burning bras and going to work was a right and pretty much required.
We're pretty different too. I'm LDS and she's Jehovah's Witness. So we do have some major differences. BUT we get along and love each other a lot.
I have friends with massive families. One of my dearest was one of 12. When I met her the oldest brother was married and had a baby on the way. The youngest was running around in diapers.
Another friend was pregnant with her next to last. She popped out that baby and when she got released the next day she went to the van, laid down in the back seat with the baby, and they drove her oldest boy across 5 states to drop him off at college. She said she'd have been laying around at home so there wasn't any difference laying in the back of the van.
One of the sweetest ladies I've ever met had 2 sons. Life was good, she and hubby were both gainfully employed as engineers in their chosen areas, and their boys were in high school. Then they joined our church. They decided to have more kids. On purpose. So they had 2 more kids. Their girl was born when the oldest was about to graduate then their boy was born when the next oldest boy was starting his first year of college.
In my opinion it doesn't make any difference to when the kids come. It matters if you don't mind having kids at that age and in those financial situations and stuff. There are millions of grandparents raising grandchildren in our country and I think they do an amazing job. So age does not matter. Situation and attitude matters.