Dave,
I'm 41 and for the last year have had aching knees and on off lower mild back ache.
I've been doing a Pilates class once a week for about 8 weeks and has helped got a book off amazon Pilates for men by david lyons jr.
http://www.amazon.co.uk/The-Complete-Book-Pilates-Men/dp/0060820772/ref=sr_1_4?s=books&ie=UTF8&qid=1340755961&sr=1-4I've just up'd to 3 times a week the class plus x2 mornings of 20 mins at home when i get up.
I am now feeling the difference.
I recommend you do a class with an instructor just to get the basics there will be mainly women their and not many men but hasn't bothered me
A common reason for Knee ache in men is usually tight hamstrings and tight hip flexors, which can also cause lower back pain.
Pilates strenghens the stomach muscles first to support back and you work outwards stretching tightness away rebalancing and working back to a fully range of motion, I really think it's great.
The guy who invented it was boxer and gymnast.
Alot of the beautiful people in showbiz do it.
I was really down a few months ago and taking pain killers (which justs masks problem and can cause liver damage over years of over using em)
But off the pain killers and started to feel alot better and upbeat.
Good luck Dave.
http://www.bodyandsoul.com.au/body+fitness/news+features/5+reasons+why+men+do+pilates,11791http://www.exercisespilates.com/blog/5-celebrities-that-do-pilates/Just found these links
Don't be put off by strange looking machines and talk of gruelling workouts, my class is just mat work and my instructor Clare is very good.
It's challenging but I don't come out drenched in sweat. (if i can do it, anyone can)
Lee