Having not reached my 4th decade, I am one of the younger users of this site and as such only my grandfather (as previously mentioned) makes it onto a census, the 1911. My grandparents were born in 1909, 1915, 1919 and 1923. So even when the 1921 census comes out, not all of them would have appeared on it! (plus two of them were born in Australia anyway)
My parents are both in their 7th decade - and both are older than Peter - but only one of their combined grandparents was old enough to be on the 1881 census - but he wasn't in the census even then as his family emigrated in 1840. My great-grandparents were born in 1878, July 1881, 1884 (x3), 1885, 1891 and 1893.
My mother is older than my father, but on balance, her grandparents were younger than his - being born in 1881, 1884, 1891 and 1893. They also had smaller families - my maternal grandfather (1909) the oldest (number 2) surviving of seven, and maternal grandmother (1915) the oldest of two.
My father's grandparents had larger families - his paternal grandfather born 1878, and he and his second wife (1884) had 9 children over 17 years - my paternal grandfather (1919) was number 7 [this particular great-grandfather was at least 23 years older than his own youngest surviving half-sibling, who was born in 1901, he was 36 when his youngest half-sibling was born in 1914 and had three children of his own]. My paternal grandmother, born in 1923 (her parents were 1884 and 1885) was the 4th of 5 - her eldest brother was born in 1915 [my grandmother is still living, but all of her siblings have died]
