is there a coach company conducting tours of approx 5 days suitable for seniors
Have a look at ATT Kings and APT tours websites. They have some guided Tasmanian tours. I have not use them so I can't comment on their quality. Also look at flight centre website. They gather a number of different tour operators under one site.
I think you will have problems.
Firstly, the duration is an issue. In five days you cannot actually get around Tasmania, so companies tend not to do tours of that duration (unless you want a boutique tour). They do shorter ones (one, two or three days) confined to a small area and longer ones (seven to 14 days) around the entire state. You need seven to 10 days to get around the island fully.
Secondly, most tour companies cater mainly to backpackers and young students without driver's licences. They are therefore not for your demographic.
The companies that might suit you have generally been mentioned. Another is Scenic - but note that their tours are for 7, 9 or 13 days. There's a message there. https://www.scenic.com.au/tour-search…
If you genuinely have a max of five days, I'd suggest you go to Hobart and do day trips with a company like Grayline who specialise in this. That way you minimise disruption of a rushed tour, can choose accommodation that suits your budget and pick and choose what you want to see.
Have a look at their day trips: grayline.com.au/australia-sightseeing/tasman…
The other option is to go upmarket and hire your own private driver and car. Let us know if your budget stretches that far. There are many companies doing it.
There are loads and loads of over 50s coach tour companies that do Tassie. My phone isn't letting me do links but just type "over 50s escorted tours Tasmania" into google.