One thing do not wear white tennis shoes or jogging suits while in Paris. The French think they are stupid and it makes you a target for pickpockets. Also blue jeans are a target for pickpockets. My family lives in France and I am there 4 times a year. Wear black jeans they fit in the best.

If you have heard that "no one in Paris wears shorts, only tourists do," it is true. I was like you. I wanted to at least fit in. Parisians tend to dress up, but you won't look out of place in most situations wearing jeans. If you are staying in a fancy hotel, plan to do a lot of shopping in ritzy stores, or want to go out to eat in a very expensive restaurant, then take along some fancy clothes for those occasions. For basic site-seeing and regular shopping, eating, etc., to fit in wear pants, skirt, or dress - whatever you like to wear. I have heard that shorts and very short skirts are frowned upon in some churches. If you want to go to a park for a day or something else like that, wear shorts and I doubt you will feel out of place. I think the only time dress is very important (except for some churches) is when you go somewhere expensive (you will likely get better service if you look like you have the money to spend or at least don't look too much like a tourist). Another pointer is to carry a small compact camera (if any) when you go into more exclusive stores and restaurants to do anything more than look around.

It looks like most people have misread your question, which asks about the flight. First, I've
been to Paris many times, plus studied there a
couple years, and plenty of French people wear blue
jeans (not just black). Lots of things may make
you a pickpocket target (fanny packs, obviously
looking like a tourist, doing dumb things with your
purse, etc.) but blue jeans alone won't do it.
It's hard to know what middle-aged is, since it can
cover about age 45-65, depending on the person using
it, but I'd say either wear some kind of comfortable
pants (i.e., khakis, jeans, Docker-type pants) or
a full, simple calf-length skirt that doesn't
wrinkle a lot or looks okay if it does.
Re some other comments: I don't think anyone should wear a sweatsuit in public ANY WHERE, let alone
traveling as it's basically not being dressed; I
believe the reference to "tennis shoes" probably
meant athletic/running shoes, which I never
wear myself and don't consider appropriate attire
for anything other than athletics/running. It will
probably not be hot enough for shorts anyway, but
I can't imagine anyone except a child wearing those
for traveling unless you're going to the tropics.
Since I often want to slip off my shoes, or my feet
expand, when on a long plane trip, I wear comfortable slip-on casual loafers or something
like that when on a plane. It is not usually that
warm in Paris in May (avg temp about 70 high, maybe
50 low at night), so be sure to have a sweater and
umbrella in an easily reachable place in case you
need it when you arrive. Actually, I just thought
of something--I have a couple very comfortable cotton knit simple pull-on dresses (full, gathered
skirt, elastic waist, calf-length) that would be
comfortable for traveling and can look quite decent
with a nice belt--that might be an idea. Lands End
catalog (and Chadwicks catalog, which I buy from) have such dresses.

The standard check-in time at Paris hotels is 12 Noon. You can also call the day before (keeping the time difference in mind) and request early check in. If the hotel is not completely booked the day before, and one of the type of room you have booked was not occupied, they are usually happy to allow you to check in early if you give them your approximate arrival time. Otherwise, you can go straight to your hotel and check your luggage, then find the nearest cafe to enjoy a beverage and snack and watch the passing parade while passing the time until check-in. By the time you arrive at the Paris airport, clear customs, collect you luggage, and make your way to your hotel, it won't be long until noontime. Wear whatever you find most comfortable on the trip over. This is not the time to be fashion conscious. Be sure to bring a sweater, as it tends to be chilly on overseas flights. I'm 47 and have refined my "packing wardrobe" (and I do not even own a pair of jeans) to the following: Black skirt, black slacks, black dress (all with POCKETS), nice jacket in my favorite color, nice v-neck cardigan in another favorite color, beautiful white or ivory blouse, coordinating tee-shirts, strand of pearls, thin gold chain, gold hoop earrings, black low-heeled pumps, and my taupe hooded (no umbrella necessary) mid-calf length trench coat. This wardrobe will take you anywhere. For visiting the tourist attractions, I include a few pairs of neutral colored slacks (tan, black) and another sweater or two, along with my Reebok walkers and/or Easy Spirit leather flats. For visiting the tourist attractions during the day, anything goes. The first thing you will learn about the weather is that it is totally unpredictable (those weather forecasts on the TV are totally useless). And, that it will change drastically throughout the day and night. We have learned to get dressed and bring along a sweater and jacket or raincoat for the day. You'll find that you add and remove pieces all day long. If you are planning dinner in a casual place or in a heavily touristed area, don't worry about what you're wearing. Otherwise, you'd be more comfortable changing for dinner. Curiously, the Parisians "dress up" to go to the park, especially on Sundays, when everyone, everywhere is dressed in their Sunday best. Everyone is also dressed up (but not to impress) on Friday and Saturday nights. After many trips to Europe, we've found that how you present yourselves does make a tremendous difference in how you are received. So, just use good judgment. The locals gaze with amusement at tourists who wear parkas when not on a ski slope, and sneakers when not on a tennis court, and shorts when not at a resort.

I'm a proponent for packing light, using neutrals (black definitely allows you to blend), and layering to accommodate variable May weather in Paris. The basic travel wardrobe that I find the most flexible is two pair of black pants (one jeans or dockers or similar, one dress trousers); one black skirt; two versatile jackets (one black - usually to match either the dress pants or the skirt - and one in a black/white tweed; several turtle neck tops (black, white, & one a bright color); a vest and/or a sweather; a black raincoat with hood (so I don't need an umbrella); two pair of shoes (one comfortable, black walking shoes & one comfortable, low heeled pair of pumps for dress); several silk scarves for color and a few pieces of costume jewelry to accessorize. These pieces provide a variety of mix-&-match options that go from casual to dressy. I also prefer the style of hidden wallet that hangs from a waistband/belt; therefore, I take only separates. On the plane, I wear/carry the bulkiest items - walking shoes, jean/dockers, the heaviest of the jackets, etc., and carry my raincoat along with a shoulder bag that contains essentials that would be difficult to replace if baggage is delayed or lost (e.g., perscriptions, eyeglasses, etc). Everything else fits into a small rolling "carryon" sized bag that is usually a few pounds over the limit for on-board carrying on international flights, but is nonetheless easy to maneuver when we arrive in Paris.