Different world/time, however you see it. I mean, some might get married young because they wanted to be official for times when separated and have something nice to go home to (same thing as my Dad and his first wife when he was a Marine) also such a high possiblitity of death they'd wanna hurry up and.. Procreate? XD
Yeah, and in Naruto's world adulthood comes earlier- reflecting Japanese culture when it still was a warrior based one- adulthood for boys and girls was right around 15, it was sort of a junior adulthood, but one could get married and start a family around then, full adulthood coming around 18. Chiyo and Tsume were around 17 (Chiyo may have even been 16, and at max 18 when Sasori's father was born) when they had their first (and only for Chiyo) child. Tsume was 4 months from her 18th birthday when Hana was born, meaning she was 16 when she conceived her. Sakura is actually 17 now, it's spring so she's just turned 17. Even up to the 1990's 16 year olds could marry in Japan. (It's not that distant in the past in the US either- my maternal grandmother eloped at 16 years old in 1932, and even now 16 year old can marry in some states with parental consent. Western culture thought of 16 year olds as junior adults who could marry, start a family and even own property at the start of the 20th century, there's residuals of this in the age one can work full time and drive a car. Our concept of the later teen years as part of childhood didn't emerge until just before WWII. My parents generation (people now in their mid-late 70's) was the first generation to grow up that way. In Japan that concept didn't begin to take hold until the US occupation of Japan (1945-52) and wasn't really fully a part of the culture until the early 1960's. Kishimoto's parents would have grown up during that time, so like me, it's possible to somewhat see both concepts of adulthood because our grandparents lived their young adult years in early transitional period.
Dream you dream alone is only a dream, but dream we dream together is reality- Yoko Ono 1971
When you go to war, both sides lose totally- Yoko Ono
Remember, our hearts are one. Even when we are at war with each other, our hearts are always beating in unison- Yoko Ono 2009