How to get an out of an old man?

I'm dating a man in is 60's and we would like to be more intimate with each other. I'm pretty much up for 24/7, but he has a declining interest. And when he is in the mood, he has trouble getting an . He's diabetic too, which I think is contributing... However, he doesn't want to take viagra due to the few cases of blindness and whatnot (he already has to wear pretty thick lensed gles and doesn't want to lose his sight; he is a historian and loves to read), which I completely understand, having had visual impairment since I was a toddler. Are there any other ways (natural aphrodisiac?) or techniques I could use to arouse him?