Changing data frame values to corresponding numbers

I'm trying to take data that appears like this.

when printed to the console and change the age groups(13-17 etc) to a corresponding number and gender (F or M etc) to a corresponding number through a loop with else if statements inside.

When I try to change given values to a corresponding number I get a key error which seems to refer to pandas not being able to find the column. But just above where I try and change it I make the new columns as the data comes in as F.18-24 or M.18-24 etc. So I make the columns by
df_pivot_table['new_age_group'] = df_pivot_table.index.str[2:7]
to separate the age group.

Now when I loop over the data in order to change say any 13-17 to 0 so Highcharts can use that as an x axis, I get a key error of '13-17' or 'F' if I'm doing gender group. From the looks of it pandas is thinking 'F' is a column when it's just a value in one of the rows. Any help on how to fix this would be huge

for i in df_pivot_table['new_gender_group']:
    if df_pivot_table['new_gender_group'][i] == 'F':
        print('female gender group')

I've tried making df_pivot_table['new_gender_group'] to a string by using .astype(str), reassigning the values to a new variable in order to separate the values in hopes that that I could track down exactly what's happening easier, changing these values after I have the final list that is about to be sent to highcharts as they're then in a list of arrays.

In order to change the column value I just needed to run df_pivot_table['new_gender_group'] = df_pivot_table['new_gender_group'].replace('M', 0) in order to replace M with 0