Not necessarily 65, only eligible for the S1 once of state pensionable age. For me that is 66 and for my wife 67.
To the OP, if you have your resedencia look into the convenio especial if you have 1 year under your belt, could well be cheaper than private cover, especially if you have exclusions that need to be taken into account.
Have a look at Jim's guides for info.
I have been led to believe once one person gets their S1 and then eligible for free state medical care partner and dependants are also eligible.
We are going to sign up for the convenio especial now our first year of residency is up. I'll have one year at the higher rate before my S1 but that is balanced by my wife being covered for free for 5 years from then until she is eligble for her S1.
I've done the sums and we will be saving over 8.000€ in that time, based on current figures.