Tablet vs. Laptop for elderly
Be wary. I think it depends on the skills and abilities of the person, not the exact age. Look carefully at every person. I have been working with a number of customers and relatives on computers for many years... this is just my thoughts... YMMV. I don't have an "answer", but some things to think about below:
Somewhere as you age it gets harder to "get" significant changes, including new technology. If a laptop or desktop is more familiar, then this may be better. If you have to change anyway (like XP to windows 7), then the tablet may be no more difficult than learning windows 7 quirks. Be careful, iPad is easier than most others I have looked at. Note that I have had great difficulty getting people (many much younger than 92!) to give up Outlook Express, which is not available with windows 7. And no, windows live is not a good match, it is significantly different. Users who could e-mail photos fine in OE can't get pictures to attach in Windows Live.
These people are smart in most cases, just this is new and it takes longer to learn... (for example, one relative who learned WordStar control key commands by himself at about age 60 on original IBM PC with two floppies is learning an iPhone now..and has a new Windows 7 computer) Almost everyone can learn, but you and they have to get past new tech changes that can appear as roadblocks.
Some elderly have more motor control with their hands than others. A tablet or iPhone requires good (not perfect) control for gestures, etc. Generally more control than a keyboard. If motor control is good, then a tablet is fine, if not it *may* be an issue. I have relatives that have issues with motor control, and the iPhone is somewhat harder to use because of that.
Note that so far the iPhone is a success with friends and relatives, but it is taking a while to learn how it works, and all the new things that go with a 4S when you are not young. (I had a learning curve on the original iPhone in 2007... and the new iPhone does more and is more complex now, so I would expect a learning curve, just be ready for that and the need for some support). Take it one step at a time. On the good side, It has sparked several 70+ users to start text messaging...so a good step forward, and much easier than most smart phones or tablets. Ease of use is critical. It is also easy to snap a picture and e-mail it...so good for all users. Note that everyone I have worked with on iPhone has good eyesight, if not a tablet, laptop, or desktop would be much better...
Look closely at the tasks that are desired, and then pick what is easiest and most familiar. This is not a simple answer, but one that needs to be looked at for each person. So far, everyone I have worked with has the iPhone or iPad as an addition to their PC...so more of a transition to new technology, may be another thought.
Sorry I don't have any "answers". Each case is somewhat unique. Good research and good luck!