26 single
In today's dollars:
Current Expenses: $9k/year (I have this posted in detail elsewhere)
Additional Work Expenses: $4k/year (gas/car maintenance/regular dry cleaning/etc)
Expected expenses for myself at retirement: $20k/year (50% increase in recreation budget, 50% increase in food budget, $5k increase in health care insurance costs that will be factored into the budget at retirement, at first it will be significantly under 5k, but later will be much more)
Expected expenses with a spouse/significant other: $40k/year (plus whatever savings she has managed to bring in by the time we retire that she can contribute to cover her additional costs)
Option 1: To reach $20k/year, I would need $540,000, and then need to adjust that for inflation, which, at my rate of expected income would result in needing ($640,000 inflated dollars). This sort of income stream is not realistic though, as I do expect to be single all my life, so I expect I need to use the income stream number I expect to need to support a spouse (option 2).
Option 2: So, to reach $40k/year, I would need $1,080,000. Adjusting for inflation again, ($1,500,000 inflated dollars)
Option 1 (which I don't intend to do, it is just a fun mental exercise), could be, with average market returns, reached by the time I am 32.
Option 2 can be reached by the time I am 36, but that assumes no workplace switches (or a workplace switch with no break in between), and I expect there to likely be one during this period, so it will likely take me an extra year, so 37.
All calculations assume all relevant standard taxes and credits/deductions, it ignores potential changes to the tax structure, and ignores one-time tax deductions such as expected annual business expenses or charitable deductions. Due to the 60+ year expected retirement, I use a SWR of 3.7%. I also assume I will move to a medium or low cost of living area, I prefer a small town/suburb setting and I am not attached to any particular state.