Same as previous posters, it is nobody else business...
I have 19 months between my 2 girls, yes the first year is hard especially with no help BUT they love being with each other. Now that my youngest is 15 months they play together much more and I can see the time they spent entertaining each other increases everyday. No quite hours yet but we'll get there eventually
Anyway, your oldest will never remember having ever been on his own and your youngest would have never known otherwise. They will always have each other to play with, fight with and gang up "against" the parents. I think it is great!
Enjoy and dont forget, having a sense of humor is absolutely necessary