Op, I wonder (kindly) if the sisters who are advising you have experienced first hand whatever situation you are currently living in?.
It’s easy for onlookers to advise if they see it from their own position of being happily married and, for example, if you are widowed. They will not have walked in your shoes.
As a widow I now have a firm lifelong friendship with a live-apart partner, with an age gap, over a number of years. If it helps, it started out as a “whirlwind” and stayed that way for a long time, then evolved into FWB, then after lockdown, now just firm loyal friends - always with the separation of our own homes and never an intention to form one household.
The age difference has presented some health and caring issues at differing times, some of which I could willingly take on, but others affected my own health and physical and mental wellbeing - and I have had to step away on occasion to protect myself.
As I see it, in middle/older age it’s lovely to gain new friendships and make the most of every day - I would say maintain your own independence, don’t hurry, take time, just enjoy what you currently have, perhaps even without needing to flrmalisd it further. Enjoy it for what it is?