Selling off above target gains rather than allocating a % to bonds based on age as a strategy

Selling off above target gains rather than allocating a % to bonds based on age as a strategy Only 29 so currently have no bonds/cash but was thinking about this as I was going through some scenarios in a spreadsheet. Basic idea is that more returns require greater risk (stock vs bond allocation) and people that have contributed well over the years eventually hit a point where it becomes smart to trade some potential returns for mitigated risk. Basic investing 101 however your goal and what you have invested should dictate allocations rather than how close you are to retirement. For example, if you are 10 years from retirement and hitting your goal would require your current contributions plus a 12% CAGR, you may see some losses with a 100% stock allocation but you will almost certainly fall short if you allocate 20%+ to bonds. However if you’re on track to have 20% more than you need with say an 8% return it would make much more sense to trade potential gains for more security. So my idea would be up to around age 40+ go for maximum gains, 100% stock allocation. For the strategy to work you need a set goal and in you’re 20s to 30s how much you need is tough to dictate as your income is probably hard to reject. After that map out contributions with a reasonable rate of return on 100% stocks (I use 8% nominal, 5% real). If your current path puts you above target, lower the initial amount until it’s just enough to hit your goal, all excess goes to bonds/ cash. Then rebalance and recalculate every year. Example with made up numbers- you have $500k, goal is $1M. $400k + contributions and 8% return get you to $1M, you allocate $400k to stocks; $100k to bonds. You contribute the amount amount you planned, say $15k end of year and get a 15% return. Per your target you needed $400k \* 8% + $15k=$447k but due to excess returns you have $475k so you sell the excess $28k in stocks into bonds/ cash. You now have $128k in bonds and $447k in cash. The next year the market loses 10% putting you off target so you use money from your cash pool to bring stock total back to target. Strategy is more appealing imo because it’s more custom to your situation and also still allows for excess gains/ earlier retirement since you could always use more. Returns are probably lower over a longer period but that is the cost of reducing risk however if market does much better than projection you still get the benefit of that via more money in your bond/cash pool. The risk reduction only limits the amount you end up with in stocks.