From the financial perspective, you need to consider the time value of money. Money today is better than money tomorrow. Growing your investments is a lot harder than growing your writing skills and starting early is the most important factor to making a lot from investments.

Don't cripple your future earning potential by not investing in your job skills. There's no guarantee that you'll ever write a best-selling novel that will make up for the potential lost income from not improving your marketable skills and having less money in the market.

The job market is also far less forgiving when you fall behind. Age discrimination is a thing and your health will not hold up enough to do the same jobs you could do when you were younger. You don't want to be doing manual labor when you're 35+ years old. You also won't have the same levels of energy when you're older and you're probably not going to want to burn the midnight oil like the 20 years olds when you're in your mid 30s.

There aren't many health conditions that will prevent you from writing. As long as you have your wits, you can still write.

That being said, you should still have enough free time to write after work if you're cutting the amount of time you spend surfing the internet, posting on Reddit, watching TV and playing video games.