I would recommend you review the following articles for more details on LTI Advantage (successor of LTI 1.1) and the current migration plan.
The short and more direct answer to your question(s) is that, for now, there is nothing preventing you from implementing over 1.1 — some vendors do not yet have a 1.3 solution developed — and there is no hard End-Of-Life date set for 2024.
When an End-Of-Life is announced, this will appear in our High Impact Changes Timeline
I hope that helps!
Learning Administration Manager