My family and I (two adults, two teenage kids) had a fantastic stay in Manolis' apartment. It is sparkling clean, very well designed and modern. The air conditioning in the bedrooms was very refreshing at the end of a long hot day in Greece, and the beds were very comfortable. The wifi was also great (something I find to be hit or miss at some locations). Of course you shouldn't be spending all of your holiday online, but it's helpful to know you have good wifi if needed!
The apartment is within a few blocks of both a great supermarket that will have everything you need, as well as a fantastic Greek bakery that you can't miss! You are only a few minutes walk to the nearest Metro station and you can get anywhere you need to be from that station. There are also many nice restaurants within a few minutes walking distance of the apartment (near the metro station). And don't miss the quiet/low traffic street right next to the apartment where you can relax and have a coffee to start your morning right!
The Acropolis is very much within walking distance if you prefer walking over the Metro, and you can also get to the major Athens highlights on foot if you're more of an active traveler. We visited almost all of the traditional sites on foot from the apartment.
The apartment is on the second level with stairs, so if mobility is a concern, check with Manolis to see if there are options for you. Otherwise, the stairs should not be a problem.