My wife and I will be visiting Paris for 7 days in September. We are in our mid sixties and have been to Paris before.
I plan to post more in the future with questions, but here are the first.
What area would be the best to stay in?
Stay in a hotel or Airbnb?
I have used both with success in Europe in the past.

For a week I'd stay in an apartment. There is no hotel that can match the convenience of a kitchen, laundry facilities, space, and comfort that an apartment offers. As for area, you'll get varying opinions. Some people prefer to be in the central core, arrondissements 1-6 and especially the areas close to the Seine, for postcard Paris, tourist-friendly restaurants, and easy acess by foot to most sites. Others prefer a more current, "authentic Paris" experience in the outer arrondissements--e.g., the 11th, the 20th. IMHO, both choices are equally valid; it depends what you are looking for. It's easy to get around the city by metro or bus; it's a fairly small city as cities go, and access probably won't be an issue for you.

You've been to Paris, so you have an idea what different parts are like. Follow your heart.

I don't agree with that at all, it's just a preference, not a fact that no hotel can match. those things. Not to mention what people are willing to spend.

Of course there are the hoops you have to jump through with private rentals, and often nonrefundable payments far in advance. And another big thing is stringent rules on arrival/departure times, with a hotel you show up whenever and if your room isn't ready, they store the luggage till it is, and you can go into the city to do stuff. Same for departure if you aren't leaving early in the morning, they will store your bags until you pick them up. I've seen many many posts from people not knowing what to do on both issues, as many private vacation rentals, you cannot check in until afternoon and sometimes late afternoon. And you may have to leave early on departure day. So that's another wrinkle in this plan, of course. But if you do this thing a lot, I guess you know that.

Are you aware that there are very stringent legal restrictions on rental apts in Paris? They have to b e registered with the city and the official registration number is suppose tyo be showing in the ad, and there are strict requirements on short term rentals due to the devastating impact such rentals have had on many urban areas, not only in France but lots of other countries/cities.

If you've been to Paris before, you should have an idea where you want to stay or what you liked the last time or didn't. My choices are not many tourists' nor first-timers or people who don't know French, etc. It's just personal preferences and taste, that's all. Which is why I wouldn't presume to tell you what you would want. The area I usually stay, many people on boards like this refer to as "so far out", even though it's just a couple metro stops and 2.5 km from Notre Dame. For first-timers, I agree staying maybe in the 4th-7th arr is a good idea. I'd stretch that a little but already some people wouldn't. And some people want to walk everywhere to all attractions, also, so that's another thing to consider if you don't want to take the metro or buses.

For example, I don't do laundry when I'm only on vacation for a week. Certainly not major clothes, I don't get that dirty being a tourist (like pants, shirts). I pack enough socks and underwear but if you must, those I do sometimes hand wash, but that's it, you don't need a laundry to do that. I don't cook on vacation, either. I'm perfectly comfortable sitting on my bed watching TV in the evening in my hotel room after running around all day/and going out to dinner or events. Not to mention, some apts can have big problems of their own you don't expect. But I think the nonrefundable and payment in advance thing is huge.

Agree with Christina. We are going for a week in late Sept-Oct, and opting again for the 5-7th arr. Very convenient to come in from CDG via the RER B and get dropped off in one of two stops -- Jardins du Luxembourg or NotreDame-St Michel. Metros convenient and nearby. We are reserved at two spots for the Fall, and refundable until two days before arrival! We love using Booking.com. As to cooking in Paris -- hah!!!

< Most desirable shops, pastries, restaurants are also located there. >

Desirable to whom?

It's a matter of personal choice. I am in my early sixties. I prefer apartments. On Air BnB there is a button you can click at the top to filter for "refundable". Also, make sure it has a license number. It will be at the end of the description.

As for area, I prefer the 5th and 6th, but I know that others here don't. I have a lovely apartment booked for May close to St. Sulpice and you can tell it is the lady's personal home.

We stayed in September 2019 in the 9th near Place Vendôme (so bordering the 1st) and found it super accessible to Metro. Quiet area since it has many offices. Would definitely stay there again.

Thanks for the replies. We have decided to go with an AirBnB in the 11th

Excellent location.

I like a hotel in the 6th and know it's a favorite of at least two other Fodorites. If you decide you want to consider a hotel, let me know and I'll share a link.

I've been lucky enough to have a semi-regular home exchange with people in the 11th, and feel very much at home there, so here's another saying it's a good choice. It covers a range of neighbourhoods, but it's mostly workaday residential and not "touristy". Can you say a bit more about where it is, in case there's any useful information to be offered?

It is just south of Square Maurice Gardette

That's not far from areas that I know quite well, but I don't have any particular detailed knowledge of it. However, I'd say that's a good choice. Plenty of public transport options - close to the metro and plenty of bus stops nearby.

I've done both, apartment and hotel. Staying one week - apartment is ideal.It is nice to return "home" and relax.Enjoy the trip.