It was over 17 years old when it went for service , it’s over 19 years old now , when I bought it I was never advised about service intervals , I’ve never read about them either , I’ve bought a few since then from a different dealer and no mention from them either, in fact your mention of five year service intervals is news to me.
Not boasting about anything , just stating a fact.
If you want to follow those guidelines, just crack on with it ,just don’t belittle those that may not agree with your point of view.