Im both jealous and glad Im not you!
Its great that your wife is amenable to working out with you, especially on an awesome and fruitful program like SS. I wish mine was. However, training with a wife/girlfriend is a known...difficulty? It can be tricky.
You should both proceed cautiously and slowly, treating your improvements as part of the fun. And getting stronger is fun. Your wife should understand that even old guys will proceed much faster than women due to certain biological realities, and that wont change. Nevertheless, I would purchase microweights as quickly as possible and treat her .5 pound strength increases as more impressive than your 5 pound gains. That should keep both of you plenty motivated.
Godspeed.