Too old? No such thing! When it comes to the breviary and variances of it, I wouldn't say "it doesn't make a difference" but since we're under no obligation to pray it in the first place, we can really pray whichever we'd like-- though of course, avoiding any conciliar (and for some, the John XXIII breviary) offices.
I pray the Pius X rubrics, Divino Afflatu.
It sounds like you've got a treasure there.