I was reading the paper Age-related accrual of methylomic variability is linked to fundamental ageing mechanisms.
There they do additional checks to see that their results are not due to differing cell type composition in blood that happens as we age.
That made me wonder, how does the cell type composition of our blood change as we age? Is it known? (I guess we would get less hematopoietic stem cells, but I do not think they are in the blood themselves.)