Rob Walling coined the "Stair Step Approach" as a way to get yourself into startups in a lower risk way: https://robwalling.com/2015/03/26/the-stair-step-method-of-b... He has also talked about it on his "Startups for the Rest of Us" podcast: https://www.startupsfortherestofus.com/episodes/episode-222-... Might be worth trying Rob's approach before leaving your job and betting the farm on a startup idea...
Do not leave your job! There are lots of ways to begin your journey to having your own company/startup.
Being employed is a great source of bootstrap funding.
I also highly recommend @DHH startup school talk. https://www.youtube.com/watch?v=0CDXJ6bMkMY
You have plenty of time. Save up and use your 'extra time' wisely.
Rob's stair step approach is a great way to get started.