You don't understand how mining works:
There will be halvings until 2140... it's just that at around 2030 the coin reward will be so small that the total supply will be mostly mined, but not 100% mined until 2140. By 2030 anyone holding 21 BTC+ will be RICH.
I don't think it's at all safe to say that 21 btc would make you rich in 2030, or at any point in the future ever. Bitcoin could become very successful and be widely adopted without its value skyrocketing. In fact, it's bitcoin's volatility and tendency to skyrocket/crash which is preventing it from gaining more widespread adoption.