It happen to me at about 45 , yep it seemed so sudden. The bifocals .... took quite a bit of adjustment. I was getting sea sick from them for awhile. It was particulary bad the day after I got them , I had to give a lecture/ speech and I kept grabbing the podium as it felt like the room /floor was moving. I think they/participants thought I was drunk. I was so embarrased.
You do get used to them .. but there is a learning curve!