Brain plasticity, window of opportunity, it’s all babble. You can learn new languages just fine as you age; the matter here is how much time you spend using the language.
The reason why adults perform generally worse than kids learning languages is mostly motivational, and not spending enough time with the language. But as an adult you got access to a bunch of resources that kids wouldn’t, such as a decent grasp of grammar on theoretical grounds, that you can (and should) use to your advantage.
Note however that watching sitcoms will likely not be enough to get any decent grasp of any language. (Otherwise I’d be speaking Japanese, given the amount of anime that I watch.) You’ll need proficiency on four levels: hearing, speaking, reading, writing.
It’s never too late to learn a language. However, French is one hell of a step coming from English.
French is my main language and even if I’ve been speaking it for close to 40 years now, I still learn language exceptions and rules today.
Still, I’d give it a go if I were you, learning something new is always fun. Enjoy!
If you want a rough comparison of the relative difficulty for a native English speaker to learn different languages, the US military’s Defense Language Institute’s guidelines are well-regarded, and they consider Spanish, French, Italian and Portuguese to be the easiest.
French is tough, but I’d argue it isn’t that hard compared to some other languages. Grammatical gender and conjugation are a pain in the ass, but the vocabulary is very familiar to a native English-speaker because of the languages’ common history (thanks, William the Conqueror)
No but at this age you should probably ask yourself at what point in life did you stoop so low as to want to communicate with the French.
/s
