Why do you want to buy them a present?
I'm in my sixties, comfortably off and honestly have everything I need or want. I really don't want to sound grizzly, but if I wanted any of the things people are suggesting here, I would have look around at what was available and bought it.
It really is the opposite of younger days, when there were lots of things I could big afford so that presents were a big thing.
If you want to acknowledge my birthday, or something special I have done for you, a card or a photo by email are perfectly lovely.
I am always interested in your lives and that of your children and grandchildren do an email about what they are up to with photos is always a welcome reminder that you are thinking of me.
People who don't do the internet often enjoy calendars and wall charts with pictures of the younger generations.
It's not just me who doesn't need anything. DH loves to give presents. MiL once said she liked perfume so he chose a new scent each birthday / Christmas. After she died, we found a drawer in her bedroom filled with beautifully wrapped bottles of scent.
The more people's houses someone has had to clear out, the less they want to accumulation throughout their lives.
Trust me in this one.