Many new vapers start at 24mg.  It's not too high if it doesn't feel too high for you.  Everyone is different.  I think you should 
vape at whatever level it takes to keep the cravings away.  Once you detox from the cigarettes and all the 4,000 other nasty chemicals in cigs, then you can worry about lowering your nicotine level if you choose.  If 24mg is too high, you'll feel it.  If you start getting nausea or headaches or feeling lightheaded, then lower it a little.  I started at 24mg and am now 
vaping 16-18mg most of the time.  Sometimes in the evenings I'll vape some 12mg 
juice.  It's an individual thing and usually has very little correlation to what you used to smoke.  Good luck.