NFP makes a big difference.
Here’s a (hopefully not inappropriate) summary of the beginning of Happy Fun Time for an NFP couple:
Day 1: RAAAWRR!!
Day 2: RAAAWRR!!
Day 3 [both of us]: I wonder what’s on Netflix?
I would encourage the OP to remember that 99% of secular sex advice is based on the assumption of contraception, sterilization, childless families, very small families, double income professional families, etc.
A practicing Catholic couple is dealing with completely different limitations with regard to their intimate life than a non-Catholic couple where one of the spouses got sterilized in their early 30s. In one’s 40s, one is looking at a risk of miscarriage that goes from 33% or so, rising into the 90s, not to mention the uncertainties and limitations of perimenopausal NFP. Plus, at some point, chromosomal abnormalities become increasingly likely:
embryology.med.unsw.edu.au/embryology/index.php/Genetic_risk_maternal_age
It’s a 1 in 66 risk at 40, 1 in 33 at 43, 1 in 16 at 46 and 1 in 8 at 49.
As you can see, the risk of chromosomal abnormality doubles every three years in the 40s.
So, it’s not exactly a mystery why one might become less interested in marital intimacy as the risks of marital intimacy go steadily up and up.