How long should they be dating for?
This depends on the individuals entirely, but in my opinion a sensible length of time would be at least 1-2 years. That really lets you know the person you're wanting to marry, particularly if you live with them.
To me, anything shorter than that is normally quite rash, unless you both really know each other, such as lifelong friends.
How old should they be when they marry?
Well, at least the legal age of consent in their country for starters.
Marrying young isn't necessarily a bad thing, but it can be difficult and rash.
My parents married young with my Dad only being 25, but having had a child at age 19 with my Mum. They've never had a falling out and have been happily married for nearly 17 years. It can work if you put enough effort into it and you love eachother.
Still being a teenager is almost definitely a sign that it's too young. You've not experienced life enough to really decide whether or not you have found someone you can commit to.
And marriage is a big commitment. Not just in choosing to not sleep with other people, but in other ways too. It often means you're putting your partner's interests on par or in front of yours, or you're commited to a family instead of your aspirations and future.
It's not so easy to carry on into education and then higher-end employment if you're married before you start. And that's something most people should aim for.
Should the man propose to the woman?
If the man wishes to.
A woman can propose too. It depends on who is ready to jump a little bit ahead and put forth the idea.
And if both are already aware they want to marry and choose a proposal as a symbolic thing in front of people then it doesn't matter who they choose to do the proposal.
Should the man blow his life savings on a ring?
Most definitely not. For Engagement or Wedding ring.
That's a terrible way to start a marriage, by spending all your financial security on something material which can be lost or stolen.
Sure, spend some money on it. A month or two's wage perhaps, but don't blow all your money on it.
Having a family is expensive, even if just husband and wife. You don't want to have nothing when you start.