Plazma isn't dosed by age or even gender. It's a matter of your size and the type (volume and intensity) of training you're doing.
A 55-year old woman training with 16 sets per bodypart five days a week could use two scoops of Plazma per session. A 28 year old, 220-pound guy doing 12 light sets of total body work three times a week might only use one.
It sounds like your current plan is on point. If you notice soreness creeping in or general recovery issues, there'd be no problem adding a second scoop. You can also ask more specific questions in the Plazma Users Forum.