Investing in individual stocks in a non-tax-advantaged account

Hi everyone, I'm a finance student looking for some clarification about personal investing. I started investing a few months ago, putting some money into individual stocks and ETFs (VXUS and VOO). I don't have a tax-advantaged retirement account since I'm not working full-time yet. I've been told that investing in a non-tax-advantaged account for the short term (<5 years) is a waste of time, and that I should focus only on building a portfolio in a retirement account once I start working. However, I know many finance students with short-term portfolios of individual stocks (not day traders/derivatives traders). I'm confident enough that I could try to time the market and build a successful portfolio of individual stocks, but I'm pretty risk-averse and don't know if spending so much time on research makes sense. Could anyone speak to why short-term investing in a non-tax-advantaged account makes sense for a young person? Should I just wait to build a portfolio once I begin investing for retirement and avoid individual stocks altogether? For now, I'm considering sticking to HYSAs and CDs.