Learning French as an adult is not the same thing as learning it as a child. Children pick up language intuitively, without having to be taught grammar, pronunciation, and vocabulary. When learning their first language, they have nothing to compare it to, and they can often learn a second language the same way.
Adults, on the other hand, tend to learn a language by comparing it to their native language - learning about similarities and differences. Adults often want to know why something is said a certain way in the new language, and tend to be frustrated by the usual response "that's just the way it is." On the other hand, adults have an important advantage in that they choose to learn a language for some reason (travel, work, family) and being interested in learning something is very helpful in one's ability to actually learn it.
The bottom line is that it is not impossible for anyone to learn French, no matter what their age. I've received emails from adults of all ages who are learning French - including a woman of 85. It's never too late!
Here are some guidelines that can help you learn French as an adult.
What and How to Learn
Start learning what you actually want and need to know
If you're planning a trip to France, learn travel French (airport vocabulary, asking for help). On the other hand, if you're learning French because you want to be able to chat with the French woman who lives down the street, learn basic vocabulary (greetings, numbers) and how to talk about yourself and others - likes and dislikes, family, etc. Once you've learned the basics for your purpose, you can start learning French related to your knowledge and experiences - your job, your interests, and from there onto other aspects of French.
Learn the way that works best for you
If you find that learning grammar is useful, learn that way. If grammar just frustrates you, try a more conversational approach. If you find textbooks daunting, try a book for kids. Try making lists of vocabulary - if that helps you, great; if not, try another approach, like labeling everything in your house or making flash cards. Don't let anyone tell you that there is only one right way to learn.
Repetition is key
Unless you have a photographic memory, you're going to need to learn and practice things a few or even many times before you know them. You can repeat exercises, answer the same questions, listen to the same sound files until you feel comfortable with them. In particular, listening and repeating many times is very good - this will help you improve your listening comprehension, speaking skills, and accent all at once.
Many people find that learning with others helps keep them on track. Consider taking a class; hiring a private tutor; or learning along with your child, spouse, or friend.
How much can you really learn in an hour a week? Make a habit of spending at least 15-30 minutes a day learning and/or practicing.
Above and beyond
Remember that language and culture go hand in hand. Learning French is more than just verbs and vocabulary; it's also about the French people and their art, music... - not to mention the cultures of other francophone countries around the world.
What and how to learn | Learning do's and don'ts | Learn and practice