You will see this in the list:
So it's 1 year and 2 months ago since the last 5.6.x release. There is an unofficial update to support PHP 7.x on GitHub if I'm not mistaken (since 5.6 doesn't run on PHP 7.x yet, officially).
There is no end date for the legacy 5.6 yet. See this quote in specific:
"Before we’d announce a end of life date for the concrete5 legacy security updates, we’d announce a stop date for marketplace sales of version 6 add-ons and themes here at concrete5.org. You should expect that to happen before too long and it’ll be a good indicator that we’re really closing the door on concrete5 legacy." - from this blog post -->
Somebody somewhere MIGHT one day try to break your stuff.
Another also strong possibility is that technology will evolve in a way that will make the old stuff stop working altogether. If your host decides to switch to PHP 7 without asking for that and you're still using legacy, your site will break.
The good news is none of that will happen overnight so you still have time to think about it and decide on the best way to deal with that. And really, you should be thinking about it.
It does have that same Object class 5.7 and 8 have that had to be renamed in 8.4 and I'm pretty sure constants are not quoted when defined so I'd say 7.2 might be an issue.