Hi Petra,
I've been turning almost for the same amount of time .... what I found ( and still do sometimes ) to be difficult, is to :
1. stop the 'tear-out' on the end-grain on the bowls & platters,
2. Match the inside curve of a bowl to the outside
3. Get a good 'sweet' transition in the internal lines from the base to the sides on a bowl.
These three things I have found the most tricky to consistently achieve... and from your photos, it seems you are 'on top' of these essentials.
I agree with the other comments about the photo's... if you could have a little more clarity & close-up, it'd probably be a bit helpful
I must say, I like the look of your apple !
For the 'relative beginners' like you and I are, - A very good bit of advice would be to keep coming back here, and read & see as much as possible from ALL the contributors, both 'novice' and the 'longer in the tooth , turning-wise' -- as the information you can pick up is absolutely invaluable, whether that is in aspects of design, techniques, pitfalls & past errors or whatever .... its great to be able to draw on the collective experience and learn
Lastly ... and perhaps most importantly.... Hello and Welcome ! Fantastic to see you here