Many people think the typical vegetarian is a teenager or someone in their twenties, but the charity Vegetarian for Life has found that 22% of care homes in the UK have one or more vegetarian residents. they have lots of support and suggestions for catering for older vegetarians on their web site.
There are also tips on getting older positively, applicable whether or not you're vegetarian.
But do remember there are lots of health benefits in being vegetarian, and many of these become more and more evident as people age.