Hi Lilith,
Health issues may not be so much at the forefront of your inquirers' minds, even though their health may play out in many (sometimes big) ways in their lives. More or less, that's true for most people at any age. If they'd like to go there, then you're wise to have an idea of areas you'll feel comfortable approaching and knowing which one's you'll feel out of your element with...and how you'll work through both scenarios.
Many people, though, may take their health--good or bad--as part & parcel, part of the bargain of living that they're willing to deal with in exchange for the bits that make life so worthwhile--things like relationships (many kinds on many levels,) career/finances (since many people are choosing/having to work rather than taking retirement,) and, really, just hope in general--of new beginnings, upcomming travel...basically anything that's possible in your life can be areas of interest in their's. If anything healthwise, health issues and the ability to have insurance/be able to pay for them can deliver the hardest blows.
Many people I know--ranging all ages, up to their 80s & 90s-- honestly feel, in mind/heart/spirit, like they're still in their 20's, even though their bodies and lives tell them otherwise. People forge new friendships, new romantic relationships, change careers, start new projects, keep studying in college, teach classes, juggle 401ks, raise children (and sometimes their grandchildren,) fall in love, change homes, are betrayed by people they've trusted or are traveling the world and trying exotic new things (some, salacious, others more mild, like taking up yoga,) or are writing their life stories in context of their newly discovered geneologies. Of the people I've known who have had their lives significantly truncated by health issues, most haven't fallen out of life completely. Being social animals, even when they're down flat, I've seen strong hearts worried/wondering about the relationsips within their family--existing/new friendships (sometimes just based on who can still drive.) Sometimes it's just enough to look forward to babies coming into the family, or pets. Transcending all the major 4 suit issues, everybody--at every age--goes though those existential moments of wondering who they are, too, what they're doing here, what's their purpose, how can they overcome what may be life-long patterns...so the Maj. Arcana helps fill these purposes.
Sorry about the long, rambling post, Lilith : ) I just wanted to congratulate you for stepping onto the fertile/enriching ground of reading for people older than yourself. It can be as rich and rewarding for you as it is a thrill and a comfort for them. Every aspect of the tarot can apply to the demographic you seek to serve.