You won't be invited to the novice network automatically anymore, because this used to invite bots, so mentors (with a crown icon) need to invite you. You can ask one for an invite (some people ask in /shout at a city).

Recently, the novice networks have got 4-8 times as many sprouts in as normal and are completely full on new players, so the mentor may have to try multiple times to invite you until a sprout logs off.