They are flaring at each other, not planning to breed. More like sizing each other planning to fight. At 19" they are not mature. Aros takes about 3-5+ years to get mature unless they were being injected with hormones.
BTW, I kinda noticed that one of them is developing a gill curl.
I kinda agree with King-eL about the flaring and sizing each other up. My asians (red and BB in particular) are doing that at the moment (much to my heartbreak). Separating them for sure today. The only difference between yours and mine is that your aros are not puffing up each other (in my case lower jaw bulge and pectoral fins flexed out to the max).
They used to swim almost in sync (i thought mating pair - yeah right) until they started doing all sorts of manuevers (crazy ivan type: swiming at each other then pulling away at the last minute), circling, swiming side by side with one leaning on the other etc etc ...it is a horrible feeling, when the lights are on they don't pay too much attention to each other, but when the lights go out the puffing starts almost immediately (used to be the other way round, when the lights were off they were chill and when the lights came on they went berzerk).
This is not the action of two silver aros about to fight. I've seen two silvers go at it and it looked nothing like this. As I said before my silvers do this occasionally yet in the 20 plus months they have been together never have they had a quarrel.