Warning: there is nudity, there is sex, and there is a lot of sweat.

This is an erotic romance between an older woman and a younger male (still in what looks like high school). The older woman needs some inspiration for her music and she finds a muse in this curious, young flower to pluck. She is the initiator in their relationship, the more impressive of our actors, and the principal reason to keep watching.
There's not a lot of story happening here, but a physical-based romance. A few tender / sweet moments, showing affection and intimacy, between Noona and our leading gent got me over the hump of calling this a mere pleasure fest. At the same time, there are a few scenes where the female lead is just on camera half-naked, then goes on the attack towards our male lead.

Only major gripe is the male lead is shown as cuddly and innocent for a longer than necessary.
A few items of Unexpected praise:
- Apart from the elevator make-out scene, it's staged really well. Lightning, her apartment, camera angles; all looking good.
- I rated the acting highly because you believe that these two are into each other. In many drama films, it's a functional surprise that the leads have feelings for each other when none of it was felt by the audience. Or worse yet, when the controlling woman character treats the younger male as a sex puppet. Neither is the case here. She digs him, despite his age, and he's into her; rightly so, might I add, because she's gorgeous, fun, and good to him.
- Character progression! Some actual maturing happens and our characters learn (some of) what they value in life.

Final thoughts:
I wouldn't go out of my way to watch this again.
It's a bit too shallow to be readily rewatchable. Exception being it may be light enough to watch with your significant other to get into the mood. The length of the film helps on the latter front.

Alternative watching experiences:
If you want an emotional rollercoaster that can get hot and heavy, try
- "Secrets, Objects" (emotion over physical) or
- "Innocent Crush" (physical over emotional).

If you want something sweeter on the heart try
- "My Little Bride" where the age gap is smaller and roles are reversed)
- "Biscuit Teacher and Star Candy", a drama series with the same roles

For something completely different try
- "Women who Flirt", for a Chinese drama film with next to no physicality (between the leads), while being funny, sweet, and really self-aware.