It sounds as though your younger dog is attempting to move up the pack, and your older dog may not be well/strong enough to enforce his position (which is fair enough at 13, he's an old man.)
I would return the toys (While supervising) and if (When) the younger dog snarls at the older dog "snarl" back immediatly and then remove the toy for 5 mins.
The idea behind this is the younger dog knows you are Pack Leader, the toys belong to you, YOU say who can play with them, and displays of agression WILL NOT BE TOLLERATED TO ANYONE.
When the dogs are playing happily, even if on oppersite sides of the room, Praise the younger dog and then the older dog, so they both know what is acceptible behaviour and neither of them becomes jealose.
If you use treats, call both dogs, and when they are both there and sitting quietly, then offer the treats at the same time (Good thing you only have two dogs or you'd need an extra hand
), again, to not inspire jealosy or dominance issues (Dominant dogs eat first). also put their food bowls down at the same time, unless food posession becomes an issue. Be as equal as possible until things settle down into the new pack order. then you can reinforce the pack order in marterial ways and (hopefully) not have to adjust your behaviour emotionally.