I question whether swimming alone can provide the human body with the required stress that facilitates optimal bone and muscle health, especially as we age. From my studies and research as a personal trainer, I believe that regular weight bearing exercises are one of the keys to healthy bones and muscles (sound diet and aerobic capacity being two others). How you incorporate this into your life and what type of exercises you do are important, as doing it incorrectly can lead to injury and diminished health.
I tend to agree with Andy, in that maximal effort training will definitely not benefit most people in the long term - especially the elderly. As far as optimal bone and muscle health goes, I advocate lifting around 80% of your one rep max - I normally suggest 5 reps 3-4 sets with at least 3 minutes rest between sets and up to 4 different exercises. I worked as a tree surgeon before becoming a TI coach, so I'm a big fan of exercises that mimic natural outdoor activity - isn't this what we were designed for?
Any weight training routine should be designed in light of your general health and exercise history. I always recommend a programme to develop aerobic fitness before introducing weight bearing exercises.
The healthiest and most agile in old age are those who include significant physical activity as part of their normal day. The difference between sedentary and active people in old age is startling - in my twenties I worked regularly with a 64 year old who could erect fence stakes faster than I could!