Is it still possible to become a professional artist, when I'm now - beeing 30 years old - only decent?

I'm going to be brutally honest with you and say that age is not your problem, but looking at the drawings you've posted here, you should be much better after 7 years of practising.

How are you practising?

I've had students like you who have been drawing for years with very little to show for it, and mostly it's because they've been drawing the same thing over and over again. That alone doesn't make you better, you need to be mindful when you practise, push yourself, branch out, learn new techniques and styles. All this will help you, even if you're aiming at mastering just one style.

Is it possible for you to become a pro? Well, I don't think it's impossible. But you need to change the way you've been approaching it so far and not waste anymore time. And yes, I'm going to suggest classes, because I'm not sure you are one of those who can do it the self-taught way.

If you don't have the possibility to take classes right now, then look into YouTube lessons, Skillshare etc. Study anatomy, light, shading, and all the other classical lessons (yes, even if you only want to draw cartoon style drawings), learn how to be critical of your own work, set yourself the goal that your next drawing must always be better than your previous one.

Best of luck! And hey, if you feel like it, why not come back in a month or so and show us what you've learned?

Based on the drawings you regularly post here then "professional artist" is not likely.

But you have improved so who can guess?

In non-Covid times especially there are clubs and societies and art shows and fairs. All over, lots of times especially in the summer. Best thing is to put yourself out there and like all artistic pursuits forget about "being a CEO". You don't just all of a sudden become "a professional artist", it is a matter of growth. My career began with being hired for a certain job, but that is another pathway....

If you put that barrier in front of you then you aren't going to get past it. 

It depends what you are doing it for it is not a trade and the skill is not for sale , its talent and what you do with it you can make it into a trade but it will always be only decent , its not a lecture just advice , enjoy just doing it is a good start