Scaling Health Runes Worth It?

So I want to learn graves really badly but I main support so I am not used to fighters. My experience with Graves so far: (have played about 10-15 games) I am super squishy and can never do enough damage to one shot people. As a result, I can't kill opponents in time before they kill me, because pretty much any attack sinks my health pretty low. I can barely win a 1v1, however if it's a 2v1 I usually get shredded. I've been running +9 armor yellows and +9 ad reds. I saw that a few pro graves players use Scaling Health per Level yellows instead of armor yellows. I read the description of the health yellows and it says I only get +24 health at lvl 18...

most games I don't even get to 18, and even when I do, how is 24 health going to help me in any way? Am I understanding scaling health runes wrong? Or do you really literally just get a maximum of +24 health out of them? I am very confused because I feel like they wouldn't be that useless since they're around 3400 ip to get a full set of them. 3400 ip for only +24 health.

p.s If this is a stupid question, just know that I am somewhat new to the indepths of league playing, i've only had one set of runes and only have a select pool of champs that I one trick, so I'm pretty oblivious to most of the stats and buffs and all that in the actual game itself. In other words, I am a noob.