Usually when I reach an artistic milestone I go to my favorite restaurant, but you could do anything really
You could even make an event here on the forums, but even something simple like buying a fancy coffee or something can help mark the milestone. I try to acknowledge my successes or achievements however I can now, because I have a tendency to downplay them 
I feel like it's been a long while! I went to college last when i was 22, now I'm 28!! (Birthday just passed a while ago) But also time feels super long for me, I have a weird time distortion because I feel like I've lived for millennia in just 6 years 
Lol Alicia!! Girl just likes cute sweaters, she can't help it 