No I didn't. I said that once you're past reproductive age, the legal status of your relationship has much less importance. That goes for polygamous AND monogamous relationships.
Notably you didn't say you wanted to marry two women.
Don't be silly. No special accommodation for old people is necessary, and the exact same institution is instituted in the exact same way. It may not be necessary to do so, but there's certainly no harm in doing so. But legalizing polygamy for older people WILL open the door for polygamy for younger people.
Look, I get that you, individually, are not hurting anyone with your relationships. But that frankly doesn't matter to this question. You're an outlier, and as far as I can tell, you're doing just fine without your relationship having any formal legal sanction. But the effect of what you do yourself, as a statistical outlier, is very different from the effect of any large-scale polygamy. And on a large scale, polygamy is incredibly corrosive to society. I'm not trying to stop you from doing what you're currently doing, but damn straight I don't want a lot of people doing it. Keeping polygamy from having any legal sanction helps make sure that remains the case.