It’ll be perfect for them. Most excursions here are either by bus or ferry and a large (not to say the majority of) percentage of tourists coming to Ushuaia are people well over their 60s, so … nothing to worry about!
Even the weather isn’t as cold as people might think and they should bring warm clothes but LIGHT .. not big boots and jackets (that would be useful if they were to trekk around the mountains).
As to the not speaking Spanish part, well … Tierra del Fuego has grown quite fast (say in the last 2 years?) as a touristic city and for that reason in most shops in town now they speak English and sometimes another language. All hotels and travel agencies have people speaking English and all guided excursions are in English too. The local tourist information city is GREAT, they are very friendly and helpful.
If you have any other questions, PLEASE, dont hesitate to ask me! gabriela.lorena(at)gmail.com

My frame of refernece is the town of Ushuaia. It is very small; most activity is on San Martin (San MAR-TEEN). Since the town is right on the harbor it is mostly flat. If you stay in town, that is. If you stay at one of the ski lodges, there are taxis readily available to take you “downtown”

Most people there speak English; I do not speak Spanish, but never had any real problem. Tourism is big there and many cruise ships with elderly patrons descend on the city.

There are many internet cafes with phones so you really do not think of yourself as in “fin de mondo.”

When you go, be sure to get ice cream from one of the local shops and get the BIG cup!

Lastly, I agree with everything Gabreila stated above. If you have other questions, feel free to email me,

grover_neuse@yahoo.com

My bet is you’ll have a great time.

Grover