Everyone, young or old - and over 70s even more- should find a person who is prepared to take dog over 'in case of need'. Our DD1 wuld take our dog on, and my neighbour would take the cat. It has to be agreed with them of course, not just 'in your head' and if possible, a fund set aside for their upkeep and vet fees.
Providing this is done, it is wonderful to have a dog companion at whatever age - as long as you choose a dog that is suited to your fitness and activity level, etc. But please, do give an older rescue your consideration - there are so many out there desperate to get a good home. One of my DDs is always putting stuff on her FB about rescues- but then chose to buy 2 expensive puppies. And so have many friends- rescue talk, puppy reality. I will never have the joy of having a puppy- but I just could not- knowing there are so many dogs out there.