I would take a different stance in relation to par and look for around 6300 yards but keep the Par at 72, looking at lengths like this:
Par 5s 475, 480, 490, 500.
Par 4s 300, 320, 340, 350, 365, 375, 395, 400, 420, 450
Par 3s 140, 155, 175, 195.
Solely I don't think you should design for just a senior player, but 375 in 2 shots is about their distance, so only 4 of those holes are really tough. Those holes are still entertaining for a flat belly though modern Par would be 69, only the 500 is really a 5, the other three make up a good combo of six strong par 4 holes.
6300 from the backs probably relates to 5500 yards from the front and most play would be at around 5700 which is good for most people because most think they like 500 yards more than they do.
Quite a lot of people really struggle to carry the ball 100 yards 'unteed up' so that would be a big consideration.
Overall my description is quite like an average UK golf course.