I'm not surprised, Pinus rigida was always incredibly expensive, but people get tetchy when it's suggested their timber is far more likely to be slow-grown, good quality, Scots pine. Whilst that might be true for the structural timbers that I tend to look at, Toby Newell said that he came across it quite regularly and that would also make sense in that he would: a) look at more floorboards than me and in more detail, and b) be likely to be able to tell the difference by sight or smell.
Anyway, essentially, rather than look for the age of the timber, I would be inclined to look for Scots pine with the same growth rate. It doesn't matter when the tree was felled, but if you try to match the number of growth rings per unit area to the existing timber, then it should behave in the same way with changes in temperature and humidity.