It might be that both of them have coincidentally lost their libido but equally it could be that one of them has and the other isnt prepared to risk what they have to make a big deal of it. When i look back over the amount of arguing and negotiating I have done with women while in a relationship just to get my leg over it leaves me scratching my head now.
Im in my mid 50s and my Mrs had a hysterectomy 10yrs ago that left her with zero libido, I know she is telling the truth because literally the week leading up to her operation we were at it regularly as we always had and after the op it just died, the surgeon said it might and for sure it did. We are a happy couple, we laugh a lots, do plenty together never argue but for me sex at home has now gone. There is very little intimacy apart from a quick cuddle and a kiss or two most days but I take satisfaction in the fact we have had 20 happy years together. If Im honest its frustrating at times and it has lead me down the path to punting I wish I had never gone but sadly thats my reality now.
Im not even sure men are programmed to shag the same women all their lives, if a marriage is based on sex and little else then its not surprising so many end in divorce
From what many of my mates say sex isnt a regular thing for them and thats without any medical issues.
As for Robbie, good luck to him, if it works for them then thats all that matters.