From your description, and general knowledge of what makes a working shepherd breed tick, my guess would be that this is likely a resurgence of mouthing behavior, and likely more related to play than aggression.
I agree that stimulating this dog's mind more is probably a good idea. I also agree that NILF is a good way to go with a dog like this.
Certainly some kind of structured game like tug or fetch should be part of this dog's exercise routine. Structured meaning that the game follows the NILF protocols- the dog needs to perform a requested behavior prior to gaining access to the resource. I generally incorporate obedience routines and tricks my dog knows.
Going off of this, I would suggest training at least once a day in obedience and/or some kind of trick behavior(s). This allows you to get fluency to incorporate these behaviors into play, and also further stimulates the mind. I'd be aiming for one meal being fed through a training session or two, and one meal being fed through some sort of interactive food puzzle toy (stuffed kong, kong wobbler, magic mushroom toy, starmark food toy, etc).
I'd also suggest a perspective shift away from this dog being "disrespectful". A Mal is a physical dog. They use their mouth a lot to express themselves- vocalizing as well as mouthing. This is their natural impulse- especially in the true, hard working lines, they've essentially been bred for grip and a desire to put things into their mouth for quite a few generations. This is not a dog that is being "disrespectful"- it is a dog that belongs to someone who has not adequately taught it how to interact with the world.
NILF is not about gaining the upper hand or showing a dog who is boss. It's about structuring the dog's life so that you have better input over their choices, and teaching a dog that they gain access to the things they want only by displaying the behaviors you request. Example: you have a chew toy a dog really wants. Dog's natural inclination is to flail around trying to get the toy, grab it from hands, grab at arms in excitement, etc. This is not a "disrespectful" dog. It is a dog who has not been taught better. You want the dog to sit nicely, wait for you to put the item on the ground, and then wait to be released. You work through this scenario by teaching the dog that it gets the thing it wants only by offering the behavior you want. You use other (still valuable) rewards to slowly build up to the end behavior. You hold the toy, the dog flails. You ask for a sit (note: sit has to be built up strongly enough for this to work). You reward the sit with food or the toy reward. If you want to push it you reward with food, then ask for a stay while the item is placed on the ground (note: stay must be strong enough to do this). You then release, rewarding with the toy.
All this is easier to solidify when a dog is still a pup, especially with this kind of dog. At 10 months, you're going to start seeing adult behaviors from this dog, and behaviors that maybe weren't such a problem as a pup are likely to escalate.
In terms of how to get a handle on this behavior, my suggestion would be to work through good basic obedience with this dog- sit, stay, down, walking on a loose leash, recall- and strengthen them to the point that they work in real life. When he gets mouthy, ask for an alternative behavior. Sit is often the easiest one. Down can be too hard for an excited (or stressed) dog to hold.
It does sound like he is playing a rough player. Your boyfriend probably plays roughly with him and he thinks you will too. maybe sit and then pet him 
