Answer 1

Read comment for explanation. Fixed version of ur code :
https://code.sololearn.com/c5CSJoKMgcrV/?ref=app

Answer 2

# Use int() function to convert the input from str to int.
s = int(input("year of your birth\n"))
v = int(input("what year is it?\n"))
# While doing operation on variables, don't use quotes.
print(v-s)
Works great