As of patch 3.3.0:

Players below level 10 may not join raids.

src/game/CalendarHandler.cpp

@@ -215,7 +215,6 @@ void WorldSession::HandleCalendarEventRsvp(WorldPacket &recv_data)
     //recv_data >> uint64
     //recv_data >> uint64
     //recv_data >> uint32
-
 }
 
 void WorldSession::HandleCalendarEventRemoveInvite(WorldPacket &recv_data)

src/game/GroupHandler.cpp

@@ -81,11 +81,13 @@ void WorldSession::HandleGroupInviteOpcode( WorldPacket & recv_data )
         SendPartyResult(PARTY_OP_INVITE, membername, ERR_PLAYER_WRONG_FACTION);
         return;
     }
+
     if(GetPlayer()->GetInstanceId() != 0 && player->GetInstanceId() != 0 && GetPlayer()->GetInstanceId() != player->GetInstanceId() && GetPlayer()->GetMapId() == player->GetMapId())
     {
         SendPartyResult(PARTY_OP_INVITE, membername, ERR_TARGET_NOT_IN_INSTANCE_S);
         return;
     }
+
     // just ignore us
     if(player->GetSocial()->HasIgnore(GetPlayer()->GetObjectGuid()))
     {
@@ -97,6 +99,12 @@ void WorldSession::HandleGroupInviteOpcode( WorldPacket & recv_data )
     if( group && group->isBGGroup() )
         group = GetPlayer()->GetOriginalGroup();
 
+    if(group && group->isRaidGroup() && !player->GetAllowLowLevelRaid() && (player->getLevel() < sWorld.getConfig(CONFIG_UINT32_MIN_LEVEL_FOR_RAID)))
+    {
+        SendPartyResult(PARTY_OP_INVITE, "", ERR_RAID_DISALLOWED_BY_LEVEL);
+        return;
+    }
+
     Group *group2 = player->GetGroup();
     if( group2 && group2->isBGGroup() )
         group2 = player->GetOriginalGroup();
@@ -938,3 +946,13 @@ void WorldSession::HandleOptOutOfLootOpcode( WorldPacket & recv_data )
     if(unkn != 0)
         sLog.outError("CMSG_GROUP_PASS_ON_LOOT: activation not implemented!");
 }
+
+void WorldSession::HandleSetAllowLowLevelRaidOpcode( WorldPacket & recv_data )
+{
+    DEBUG_LOG("WORLD: Received CMSG_SET_ALLOW_LOW_LEVEL_RAID: %4X", recv_data.GetOpcode());
+
+    uint8 allow;
+    recv_data >> allow;
+
+    GetPlayer()->SetAllowLowLevelRaid(allow);
+}

src/game/Opcodes.cpp

@@ -1314,8 +1314,8 @@ OpcodeHandler opcodeTable[NUM_MSG_TYPES] =
     /*0x505*/ { "UMSG_UNKNOWN_1285",                            STATUS_NEVER,    PROCESS_INPLACE,      &WorldSession::Handle_NULL                     },
     /*0x506*/ { "SMSG_CORPSE_IS_NOT_IN_INSTANCE",               STATUS_NEVER,    PROCESS_INPLACE,      &WorldSession::Handle_ServerSide               },
     /*0x507*/ { "UMSG_UNKNOWN_1287",                            STATUS_NEVER,    PROCESS_INPLACE,      &WorldSession::Handle_NULL                     },
-    /*0x508*/ { "CMSG_SET_ALLOW_LOW_LEVEL_RAID1",               STATUS_NEVER,    PROCESS_INPLACE,      &WorldSession::Handle_NULL                     },
+    /*0x508*/ { "CMSG_SET_ALLOW_LOW_LEVEL_RAID1",               STATUS_LOGGEDIN, PROCESS_INPLACE,      &WorldSession::HandleSetAllowLowLevelRaidOpcode},
-    /*0x509*/ { "CMSG_SET_ALLOW_LOW_LEVEL_RAID2",               STATUS_NEVER,    PROCESS_INPLACE,      &WorldSession::Handle_NULL                     },
+    /*0x509*/ { "CMSG_SET_ALLOW_LOW_LEVEL_RAID2",               STATUS_LOGGEDIN, PROCESS_INPLACE,      &WorldSession::HandleSetAllowLowLevelRaidOpcode},
     /*0x50A*/ { "SMSG_CAMERA_SHAKE",                            STATUS_NEVER,    PROCESS_INPLACE,      &WorldSession::Handle_ServerSide               },
     /*0x50B*/ { "SMSG_UPDATE_ITEM_ENCHANTMENTS",                STATUS_NEVER,    PROCESS_INPLACE,      &WorldSession::Handle_ServerSide               },
     /*0x50C*/ { "UMSG_UNKNOWN_1292",                            STATUS_NEVER,    PROCESS_INPLACE,      &WorldSession::Handle_NULL                     },

src/game/Player.h

@@ -510,7 +510,7 @@ enum PlayerFlags
     PLAYER_FLAGS_NO_PLAY_TIME           = 0x00002000,       // played too long time
     PLAYER_FLAGS_IS_OUT_OF_BOUNDS       = 0x00004000,       // Lua_IsOutOfBounds
     PLAYER_FLAGS_DEVELOPER              = 0x00008000,       // <Dev> chat tag, name prefix
-    PLAYER_FLAGS_UNK17             = 0x00010000,            // pre-3.0.3 PLAYER_FLAGS_SANCTUARY flag for player entered sanctuary
+    PLAYER_FLAGS_ENABLE_LOW_LEVEL_RAID  = 0x00010000,       // triggers lua event EVENT_ENABLE_LOW_LEVEL_RAID
     PLAYER_FLAGS_TAXI_BENCHMARK         = 0x00020000,       // taxi benchmark mode (on/off) (2.0.1)
     PLAYER_FLAGS_PVP_TIMER              = 0x00040000,       // 3.0.2, pvp timer active (after you disable pvp manually)
     PLAYER_FLAGS_COMMENTATOR            = 0x00080000,
@@ -1789,6 +1789,8 @@ class MANGOS_DLL_SPEC Player : public Unit
         static void RemoveFromGroup(Group* group, ObjectGuid guid);
         void RemoveFromGroup() { RemoveFromGroup(GetGroup(), GetObjectGuid()); }
         void SendUpdateToOutOfRangeGroupMembers();
+        void SetAllowLowLevelRaid(bool allow) { ApplyModFlag(PLAYER_FLAGS, PLAYER_FLAGS_ENABLE_LOW_LEVEL_RAID, allow); }
+        bool GetAllowLowLevelRaid() const { return HasFlag(PLAYER_FLAGS, PLAYER_FLAGS_ENABLE_LOW_LEVEL_RAID); }
 
         void SetInGuild(uint32 GuildId) { SetUInt32Value(PLAYER_GUILDID, GuildId); }
         void SetRank(uint32 rankId){ SetUInt32Value(PLAYER_GUILDRANK, rankId); }

src/game/World.cpp

@@ -847,6 +847,8 @@ void World::LoadConfigSettings(bool reload)
     if (configNoReload(reload, CONFIG_UINT32_GUID_RESERVE_SIZE_GAMEOBJECT, "GuidReserveSize.GameObject", 100))
         setConfigPos(CONFIG_UINT32_GUID_RESERVE_SIZE_GAMEOBJECT, "GuidReserveSize.GameObject", 100);
 
+    setConfig(CONFIG_UINT32_MIN_LEVEL_FOR_RAID, "Raid.MinLevel", 10);
+
     ///- Read the "Data" directory from the config file
     std::string dataPath = sConfig.GetStringDefault("DataDir", "./");
 

src/game/World.h

@@ -187,6 +187,7 @@ enum eConfigUInt32Values
     CONFIG_UINT32_CHARDELETE_MIN_LEVEL,
     CONFIG_UINT32_GUID_RESERVE_SIZE_CREATURE,
     CONFIG_UINT32_GUID_RESERVE_SIZE_GAMEOBJECT,
+    CONFIG_UINT32_MIN_LEVEL_FOR_RAID,
     CONFIG_UINT32_VALUE_COUNT
 };
 

src/game/WorldSession.h

@@ -482,6 +482,7 @@ class MANGOS_DLL_SPEC WorldSession
         void HandleGroupSetLeaderOpcode(WorldPacket& recvPacket);
         void HandleGroupDisbandOpcode(WorldPacket& recvPacket);
         void HandleOptOutOfLootOpcode( WorldPacket &recv_data );
+        void HandleSetAllowLowLevelRaidOpcode( WorldPacket & recv_data );
         void HandleLootMethodOpcode(WorldPacket& recvPacket);
         void HandleLootRoll( WorldPacket &recv_data );
         void HandleRequestPartyMemberStatsOpcode( WorldPacket &recv_data );

src/mangosd/mangosd.conf.dist.in

@@ -729,6 +729,11 @@ LogColors = ""
 #    Motd
 #        Message of the Day. Displayed at worldlogin for every user ('@' for a newline).
 #
+#    Raid.MinLevel
+#        Minimal player level to join raid groups (only affects existing raid groups, party->raid convert ignored)
+#        You can bypass this setting by typing "/script SetAllowLowLevelRaid(true/false)" command in chat
+#        Default: 10
+#
 ###################################################################################################################
 
 GameType = 1
@@ -797,6 +802,7 @@ BeepAtStart = 1
 ShowProgressBars = 1
 WaitAtStartupError = 0
 Motd = "Welcome to the Massive Network Game Object Server."
+Raid.MinLevel = 10
 
 ###################################################################################################################
 # PLAYER INTERACTION