When the co-op Whirlwind was originally added to the game there was a minimum level at which you could accept any invites to this co-op. Players below level 46 could not accept.
Yesterday while on a invite myself a level 37 player got invited, poor guy had neither the gens or troops to take part. I can only conclude that at some point since unity was introduced that the mechanic to prevent low level players taking part in a high level co-op got broken.
Unfortunately since the introduction of Unity it can take up to 20 minutes before a new friend appears in your friends bar unlike in the flash days when they was added instantly. This means we have no way to ensure that inappropriate invites are not sent out.