We're attending our first one with Ellie later in February. Sadly, the Atlanta area is the closest place for Bully meetups for us and that's a good 1.5-2 hour drive each way. One meetup group is having a meetup closer to us that will only take about 45 minutes to an hour to get to, so we're going to try it out.
As long as Henry's up to date on his shots, flea/tick/heartworm preventative, etc, I'd think 5 months should be fine. Even though others may not have theirs up to date, you don't want to bring home any unwanted guests.
There's also a Bulldog Meetup forum on the main forums page that may have some good info as well.