My wife is an elementary school counselor, and we've always been totally frank with our kiddo on the good and bad in life. When pets have died, we've explained the death and we've been sad about it together - because it IS sad, and it affects all of us. We ask our daughter how her day was (she's 6) and at this point she's been "trained" to query the same of us.
I don't think there's any age where it's appropriate to start this; the answer is pretty much ANY age. Don't shield your children from the joys and sadnesses in life, they are real and will be a perpetual part not just of their upbringing but their life in general. My daughter's first fish death occurred when she was 3. We buried him, wished him well and thanked him for being a part of our family. In the coming years, we expect my wife's grandmother to pass and that will be the REAL test for us on how we handle that kind of sadness.
And with regards to joys there are daily experiences to be reveled and cherished with our kids, no matter how trivial they are, and children should know how precious and wonderful life is by pointing out the daily good things to balance out the sorrows. We celebrate a good spelling test with reinforcement, we endeavor to improve the math grade, we look at life as an opportunity to improve who we are and the world around us. Dwelling only on the practical to me seems to negate what it is that makes us feel alive and a part of something.
Teach your kids to embrace the joys and the sorrows - it's who we are, and it's how we know we're alive. And maybe in turn that will help you therapeutically recognize more of the joys and cope with the sorrows through your kids that in my humble opinion were unfortunately neglected in your own upbringing.