I think that your query settings are not taking effect because they
are not being passed to GetYouTubeUserFeed. It looks like the call to
GetYouTubeUserFeed only includes the username, but you should be able
to use max_results and start_index if you use:
userFeed = client.GetYouTubeUserFeed(uri=query.ToString())
You will need to add the username to the feed string in the query
object, since the method will ignore the username when you pass in a
uri. Please let me know if it doesn't work :)
Happy coding,
Jeff