At what stage in life should I stop focusing on my career & focus on investing well instead?

When you have a sizeable amt of capital, say 100k to invest

At the point when managing investments is part of your job.

Otherwise, you will always be a part-time trader trying to fight against full-time traders. It seems better to me to just invest passively and spend your time and energy on your job, which is presumably what you are good at and have a better chance of excelling in.

Depends on your investment portfolio. For decent investors, generating 10% p.a. consistently is not too difficult. So if you already have a portfolio of 2M and above, you could generate more than your current income.

The first thing u need to do is to do a reality check on your liabilities. Liabilities include mortgage, car loans, insurance premiums, and the cost of feeding your household until your kids become self sufficient.

Since your current pay was achieved only recently, just by labour income and saving alone it is unlikely u have any substantial net worth after accounting for taxes, cpf and expenses. Investing well does not guarantee u come out alive as for you there is a need to put huge sums of capital at risk for it to have a meaningful return to your life. Huge capital meaning many many years of your current savings. Therefore even small percentage losses from investing can represent many months of savings lost, whether u can stomach that volatility is only something u need to experience for yourself. My experience with people who have 2 kids to feed etc are that this ability to withstand volatility is close to zero unless they have been in this long before starting a family.

Maybe you can monetize your other skills and develop non investing income streams, start a small biz etc. I say all these assuming u are not the sole breadwinner. If you are, then the entire conversation above is invalid