My first domain got sold in 2020, within 3 months of registration. Yes, it was a new domain, hand registered (but very well thought out and background researched) - this is what got me into domaining with my both feet in.
First website I ever created was back in 2003/2004 and I'm a professional web developer since 2006. I started working with things like web content creation, inbound marketing, SEO & Big Data since 2009. So I worked with and around domains and websites for a very long time and owned some domain names to develop later; but I was never really into domaining until that first sale.
Since then I've learnt many things about domaining. I'm still learning & I believe I have many more things to learn in the areas such as pricing & marketing, but I think the most important understanding I've gained is the fact that you need to have patience if you want to earn big from domaining. Fortunately for me, as a developer who is well versed in content creation and SEO, I know exactly how to monetize some of my domains so that I can hold all of my domains indefinitely without worrying about finance.
So average holding time is not an important metric for me at all. IMHO, the sooner people realize and can deploy a strategy like this, the sooner they'll learn to enjoy domaining.