Poll about birth spacing. Whoever is closest to you in age, whether older or younger.
21 years
My sister is 15½ months younger than me. Irish Catholic Mom. Eisenhower administration.
Eleven years.
He’s six years younger than me.
I have one sister and she’s younger than me by 15 months.
Irish Catholic mom (and dad). Eisenhower administration. My sister is 11 months younger than me.
I’m the youngest by 11 1/2 years (or as I do, round up to 12, much to sis’s disapproval). 
I have a friend who is the youngest by 10 months. Catholic, but in the Philippines.
Im the only. 
I am the youngest by 8 years.
Older sister is 4.5 years older
Older brother (deceased) was 3.5 years older
Younger sister 22 years younger
Fourteen months older and twenty-four months younger.
Two years older, to the day.
I am 10 months and 3 weeks younger than my brother. Parents not Catholic, just horny.
Fifteen months. Irish Catholic mom and dad. Johnson administration.
Twin posts. Heh.
My twin sister came out seven minutes before me.
Older brother is about 4 minutes older.
14 months. Jewish mother who carefully planned her children for minimum career impact.
I’m 2 years 11 months older than my only sibling.