Mine was like that, too. Sometimes even if I tried open-ended questions, he just gave short answers. And once he got older, I tried a lot to extend conversations because I never knew which might be the last. But most of my favourite memories with him are just doing things together - gardening, woodworking, once we drove out somewhere and just enjoyed to view in silence. Having something to do with your hands can sometimes make conversation easier. Asking to see his photo books is a good one, too, because he can tell you the background of the photos.

If you need ideas, just googling "questions to ask your parents" will get you a good list of potential convo starters and of course taking an interest in his work, hobbies, other things he likes helps. Don't be too hard on yourself if he just isn't the chatty type, though.