At what age is someone diagnosed with schizophrenia

it can occur at any age, the average age of onset tends to be in the late teens to the early 20s for men, and the late 20s to early 30s for women

Explanation:

to answer your question:

f(x)= a^x.  if x=0, f(x)=1  if x=1, f(x)=a  if x=1, f(x)=a^a