Blood does get old along with your body.
However your body does replace that blood with new blood overtime and just like when you lose some blood through a cut your body will eventually replace those blood cells and blood.
The average life span of healthy red blood cells (RBCs) is 120 days, but that can be shortened in pathologic conditions including sepsis and in illnesses like sickle cell disease that interfere with normal production of RBCs.
Not every cell in your body replaces itself but most cells do replace themselves.
However most cells in your body do replace themselves every 7 to 10 years so you are constantly getting new cells in your body over the years.
However some of your cells will be as old as your body and will stay with your body until you die.
Some of the bodies cells never get replaced from birth and until death but most of the bodies cells do get replaced.
The human body does replace itself every 7 to 10 years.
Although it's not in the way that some people may think.
For example you're not actually getting a new body every 7 years or so but instead your cells in your body are reproducing and replacing themselves and rebuilding themselves every 7 years or so.
You'll usually notice significant changes in your bodies appearance such as in your face as your face change every 7 to 10 years.
So you may look different 7 years from now.
Your face changes much more quickly from the time you're born and until you turn 18 and then the body changes at a slower rate.
When you're an infant and then reach 1 year old to 2 years old you'll notice a huge change in your faces appearance as well as you've grown a lot in those years.
Your body and face are constantly changing over the years without you even realizing it.
Your bodies cells do reproduce at a nonstop rate, but you're not a new person every 7 years especially after you turn 18.
You still have the same body but your facial features can change and your body can still grow out wider.