We (a couple, 31&32 years old) stayed in the apartment for about a month. We enjoyed our stay very much. A few things to know abour the apartment:

On the plus side:
- location is great, close to San Telmo attractions and center, but rather quiet due to being in the center of a block
- the atmosphere of the house is good, we met nice other guests
- the hosts are nice and helpful
- beautiful apartment, interesting architectural details, great terrace to relax

Caveats:
- Not overly clean. This is Airbnb and we don't expect five star cleanliness. But although the apartment had been cleaned before we moved in, some areas apparently hadn't been cleaned for a long time (e.g. on top of the wardrobe, some kitchen shelves, decorative elements) and were therefore greasy and/or dusty.
- It's an old house. At the time of our stay, there were several ant roads along the walls of our apartment. Small ants, and they stuck to their roads, so not overly bothering, but still. Also, we killed the occasional cucaracha with the spray provided. One time, there was water dripping from the ceiling because the pool located above was leaking (Emilio said this was the first time that happened).
- On some nights (maybe twice per week?) sessions with rather loud music are hosted in the early evening (duration ca. 2 hours)
- Kitchen could be better equipped for a long term stay, otherwise fine

If you can live with all that, we would certainly recommend staying there. We had a good time and would book it again.