At age 0, you have no elements in your array of years. So the first year is also element 1.
If you want code to reflect the way you've done counting and arithmetic your whole life, you'd want it to start at 1.
Which to me is one step away from using the timepoint as the index iteself (zero as start), verus (1 year from zero).
How would you index the time before the first birthday?
