Hi ArtnBarb,
My chum Eleanor, who contributes regularly on SE, suggested I respond to your questions..... she know that my wife and I are wildlife conservationists, photographers etc. We tend to fly to far off places, whilst we are still fit enough, so that answers one of your questions.... of course you are not too old, we are pretty much the same ages as you two! Yes, it is a little bit of a risk travelling long distances as you get older, but decent travel insurance will give you peace of mind.
Can I suggest that you look at my article on Slow Europe :
https://www.sloweurope.com/community/threads/a-beginners-guide-to-safari-holidays.3099/
Without repeating myself too much, I really would recommend Northern Tanzania, the Serengeti and short grass plains, Ngorogor Crater, Tarangire and maybe Lake Manyara. The Serengeti is a must for cats, plus Ngorogoro (you will definitely see them in both places), and the last time we went (2017), we lost count of the number of elephants we saw in Tarangire ( 150+ I think). As said in my article, there are many places to see wildlife in Africa, not least South Africa, Namibia, Botswana, Uganda, Kenya, etc, etc., but a properly planned route through Tanzania will be the best for your first safari holiday... and best value, although with the latest national park fees it is not cheap.
When you say organized...... yes, they certainly need to be organized or rather planned well. If you go with a well known UK tour operator, it will be anything from a small group of say six people to up to 15-20. It very much depends whether you are very keen wildlife photographers or not, as a six or eight person 4x4 vehicle can be a little crowded and not everyone wants to stop or stay in that in that one place as long as you do, so it can be a little hit and miss with your photography. The consensus prevails and it can be frustrating.
You can always arrange and plan a private safari for two but of course this will be more expensive. We use one of the 'ground agents' in Arusha (Tanzania itself) who UK travel agents subcontract you out to. We go direct and save a lot of money, thus making our private safaris affordable. The other aspect, which is very personal preference, the travel companies will always introduce some 'culture' into the trips, ala visiting craft factories, traditional villages, watching Masai 'warriors' jumping, etc. Whilst this does give the local communities some trade, you feel compelled to purchase things you may not want. You contribute to the local economy just by being there. It is also a way of keeping the holiday costs down as the safari /game drives, plus driver/guide costs, and the now very high national park fees, are the major part of overall cost. With a private /bespoke safari holiday, you can pick and choose what you want to include.
Time of year..... certainly in the Serengeti, the vast short grass plains are abundant with wildebeest calving in February/March, and later they move North up towards the Mara River and into the Masai Mara itself in May/June. There are of course plenty of big cats around at his time, so the movement of the 'prey' animals is important.... plenty of zebras and giraffes as well at this time, they share the same areas.
We are going to Ethiopia this Autumn and Tanzania again in early Spring 2019. If you want any further information on anything to do with wildlife type holidays, who to book with, etc., please get in touch by email if you wish:
grahambrace1946@gmail.com