lastest_x_qs.py

import operator
from django.db import models
from django.contrib.auth.models import User
from myapp.models import License


or_list = []
values = User.objects.values_list('id').annotate(models.Max('licenses__created_at'))

for pk, dt in values:
    or_list.append(models.Q(user__pk=pk, created_at=dt))

qs = License.objects.filter(reduce(operator.or_, or_list))

for license in qs:
    print license.id, license.created_at, license.user.username