I suggest to support the muscle build and weight loss, do it like me and go to Bikram Yoga, that is in a hot room and I tell you, it's tough, but does you good and there are many nice girls to motivate you, too :lol:
It sounds good, I've tried a bit of yoga in the past and quite liked it (there were lots of women, but most were even older than me :( :lol: ).
But I'm not sure my back could take it now - I $%&#ed it up somehow a few years ago and developed the habit of sitting/slumping really badly to stop it hurting. I couldn't do any type of situps anymore because they hurt my back, and now my stomach muscles have totally gone to sh!t. I've got so little strength and flexibility in my "core", it's an absolute joke.
It's a common misperception that you couldn't do Yoga with a bad back or bad knee. The opposite is the case, yoga will heal your posture and strengthen your back and knee muscles, creating a core stability that will remove your pain over time. Through the heat, you're also supported in terms of flexibility (and you sweat more), so that it helps pushing yourself that little bit further everytime you go.
Sometimes there are older ladies, but well enough of them are in their 20s and 30s, and they look after themselves rather well :)
Here is a list of all studios worldwide, maybe there is one close to you:
www.bikramyoga.comAlternatively, there are some independent studios that do the same 26 postures routine in the hot room, but call themselves "Hot Yoga" (to not having to pay royalties to Bikram, the guru).
I'm sure there's gonna be one of either within reach. Go min. 3 times a week and things will significantly start to change after 1-2 months.