Django: Age declension template tag

age_declension.py

@register.filter(name="age_declension")
def age_declension(age):

    end = ''
    num = None
    
    if age >= 5 and age <= 14:
        end = 'лет'
    else:
        num = (math.floor(age/10)*10)

    if num == 1:
        end = 'год'
    elif num == 0:
        end = 'лет'
    elif num >= 2 and num <= 4:
        end = 'года'
    elif num >= 5 and num <= 9:
        end = 'лет'

    age = str(age)
    return age + '  ' + end