Cynically speaking: the people making those laws probably don't want to be impacted by it. And Germany is effectively a gerontocracy.
CDU are losing popularity if we are to believe press, so that is one of the populist ways to boost some numbers for elections.
Oh and they've added a very political clause: the government can activate conscription WITHOUT a parliament vote. So most political parties who have voted in favor of conscription want to be able to claim "it wasn't us, it was Merz" (ie. CDU). In reality CSU and SPD have voted to effectively conscript German men between 18 and 45.
In other words, Germany expects to be in open war in a matter of months to years. Like every country before them they've decided young men are cheaper than actually investing in military equipment (they're investing in military equipment, but they just won't have it in that time period)
This probably means that if you can get out, get out, because it's not like being 46 years old will protect you from the impact of that, and yes it's not clear what the timing is going to be, and they're not being very forward about what the reason is for conscription.
So that's why 45. Because the existing conscription law (1954 + 2025) allows for conscripting every German male between 18 and 45.
But the US, for all its militarism, and all its military adventures, has not used the draft since Vietnam.
So I would say that Germany sees the need to be in a position where it can respond quickly if they need it. Well, given current events in their neighborhood, I can see their point. In fact, I would say that they are probably at least three years late in doing this.
Let's start with an easy one: Will Germany be ready (war is more than cheap bodies, after all, equipment, plans, ...)? No, they won't. They've never been ready before.
Will the US help? That was a given even just 1 year ago, but now is strongly in doubt.
What will Germany's reaction be to the European states that just don't help?
What will happen to world trade? The question is who will save it, because the historical answer was of course US.
>Will the US help? That was a given even just 1 year ago, but now is strongly in doubt. With the current commander in chief, the US will do nothing except talk a lot of nonsense contradicting itself daily.
>What will happen to world trade?. World trade as we know it is done. National security interests will force strategic industries to be on-shored. New trade deals will only be made with a short list of trustworthy allies.
If Russia does attack, the US will take 1+ years to ramp up and we will take a long time before we reach Europe in large numbers. The rapid reaction forces we have are not prepared for the new way of fighting we see in Ukraine.
Also the main reason russia is still slowly gaining land in Ukraine is because there are not enough people to man the frontline.