I have always had an interest in genealogy, but recently I decided I would use the skills I've developed to create family histories for some of the care home residents I work with. Today I handed over two completed histories (in the style of This is Your Life) and it almost moved me to tears to see the total joy they brought to the recipients. In addition to the more mundane births and marriages I used plenty of old photographs and included lots of peripheral, but interesting details; photographs of houses where relatives had lived, further details about some of the jobs people did, newspaper articles, old maps etc. I even found a wonderful photograph of a 92 year old resident's grandmother, a photo of a very grand house where another resident's dad had been born and details of ancestors that had lived abroad; plus war records and some very detailed prison records from 1848. One resident had an ancestor who, when he died, had 100 coaches and 400 men in the funeral procession.
Almost all of the residents were engaged and asking questions as I shared the information from the files I'd compiled, and after they'd been handed over I was humbled to see their new owners poring over them. I have come away with requests from other residents asking me to do their families too and there is so much now that's online I've already found some treasures for my next family history.
So, if you're stuck for something interesting to do with an elderly relative I really do recommend you have a go at doing a family tree. 
Off to bed asap I think.