jinja2 first x items in for ... if loop
to skip the first x elements you can
{% for category in categories[x:] %}
with all the expressions you can use for the regular lists
EDIT:
you can simply nest the expressions?, i.e.
{% for item in list if item.author == 'bob' %}
{% if loop.index <= 5 %}
do something
{% endif %}
{% endfor %}
You can also use
{% for item in list[0:6] %}