You have to receive the heirloom first before you can unlock it. The only way to get an heirloom is by retiring your Sims. Unfortunately, I can't assure you'll get the Unfinished Fashion Opus heirlooms since sometimes, I'm getting a duplicate or something I don't need.

How do you retire your sims ? What the frick is retire?

You unlock retirement when you reach level 14, retirement is when you let your current adult sims pass into the next stage of life (elder) or they age up and leave the household, and then they leave a heir loom

Level 16*

I'm already at level 19 with all the traits and maxed out hobbies but mine still doesn't have a retire button. I'm using android. Please help.

They have to do events until they can retire. Think of it as a 5th trait: you still need to fill up the bar to unlock it