Use:
subset(data, :AGE31X => a -> a .== 46, :percentile_label_Platinum => R -> R .== 35)
or
filter([:AGE31X, :percentile_label_Platinum] => (a, R) -> a == 46 && R == 35, data)
or with DataFramesMeta.jl:
@rsubset(data, :AGE31X == 46, :percentile_label_Platinum == 35)