Creating New Theme not possible

Hi, I am fairly new to Grav and CLI in general. I was looking forward to working with Grav as it seemed quite straight-forward. While trying to create a new Theme with the tutorial from the docs, I faced this issue which I don't even understand... :(

Parse error: parse error, expecting '&'' or"variable (T_VARIABLE)"' in /Applications/MAMP/htdocs/grav-admin-wrk-01/vendor/symfony/var-dumper/Resources/functions/dump.php on line 18

I cannot make any sense of this. This happened after I installed a clean Grav (Skeleton of Cactus with manually installed Admin panel). Then I installed the devtools plugin via admin panel. After that I started the Terminal and went to the root of Grav (the above grav-admin-wrk-01 folder, typing in bin/plugin devtools new-theme – and that's when everything went off.

I use macOSX 10.11 with MAMP (freshly installed) as a server environment. Idk if it helps, but this is what php -v gives me back:

PHP 5.5.38 (cli) (built: Oct 29 2017 20:49:07)
Copyright (c) 1997-2015 The PHP Group
Zend Engine v2.5.0, Copyright (c) 1998-2015 Zend Technologies

Even though MAMP states PHP Version is something 7-ish

It does look like a PHP version problem. You possibly have both installed and the CLI is running 5.x. To be sure, create a file called info.php and place it in the same Grav folder where index.php is. Then add this to it:

<?php phpinfo(); ?>

Then load it into your browser from http://<yourtestsite>/info.php.

That will tell you which version MAMP is running.