What does it matter if a person wants to take their time to learn a language, to have fun with it, to pass the time with it. In theory there is nothing wrong with that idea. In practice it is a dishonest idea.
Let’s say you asked about the “brow of the hill”, the earliest point at which it is more fun than work to maintain your language. One early point might be texting with a friend.
It’s very hard to find texting fun with under 1200 words of a language because there is almost nothing that you can talk about. But over that, you’ can start having fun, and once you get to a vocabulary of 2,000+ you would certainly be having lots of fun or you certainly could be, assuming you have fun friends.
If you are learning (& not forgetting) 10 words per day, that is 120 days to reach “minimal fun” (or 200 days to reach “lots of fun”). Call it 180 days for easy arithmetic – that is 6 months. Maybe you can hold out for 6 months on the wrong side of the brow of the hill – where things are more work than fun. Maybe. Lot’s of people can’t though because most adults are consuming their emotional energy each day on other things (work, family & more) thus few people have much ‘left in the tank’ by the time their free-time comes around. Maybe you could. Maybe.
Now let’s we do the same calculation, using more conventional learning. Using a traditional approach, you are unlikely to learn more than 3 words per day – that is you might learn more each day, but you will increase your vocabulary by NET 3 words per day, AFTER taking words forgotten into account. That means more than a year (400 days) to reach “minimal fun”. Maybe you can manage that, I don’t know. I do know your odds of sustaining your enthusiasm for 120 days are much, much greater than for 400 days.
The faster you can learn the more likely you are to succeed. Point blank. No discussion required. Because it is obviously true that sustaining motivation and effort for a short time is easier than doing so for a long time. Never let that be far from your mind. The most useful thing you can do if you want to learn a language is learn how to learn a language faster than you do today. The dividends are many. Improving your odds of success being the most important.