Composing URLs for fetching passenger fares from multiple providers
You can definitely simplify some things. For example, determining the ages variable:

kid_age = ''
if len(pax['ages']) &gt; 0:
    for age in pax['ages']:
        kid_age += str(age) + ','
    kid_age = kid_age[:-1]
ages = 0 if kid_age == '' else kid_age


can be done in a single line and str.join():

ages = ','.join(pax['ages']) if pax['ages'] else 0


Some other notes:


docstrings should be enclosed in triple double quotes, not single quotes
I would move create_link from out of the function to "helpers" or "libs"
define your format_url format strings as constants and move to the module level
follow lower_case_with_underscores variable and method naming convention 
define your date format as a constant as well - this way, if it changes, you would make a change in a single place only