Looks good for a beginner! however you’ve got some array out of bounds exceptions there.
you reference the arrays “months_previous” and “months_to_come” up to an 11th index whereas these arrays are sized less than 11. For example your “months_previous” array has only 4 strings contained within it, so calling months_previous and higher will result in an out of bounds exception.
second, you can significantly reduce the size of your program by using loops, doing so can also mitigate your out of bounds error by telling the loop to only iterate as many times as there is data available, like so:
for month in months_previous:
if month_birth == month:
print("\nYou are " + str(calcAge) + " years old " + name + "!")
that alone would remove 11 of your elif statements :)
I actually made an age calculator in python a while ago, feel free to take a look at it! https://code.sololearn.com/cwZe6m7Lp5Nx/?ref=app