Start before the money is worth managing
The standard advice is to wait — earn first, invest seriously later, once the sums justify the effort. I think that's backwards. Capital is the least important input at the start.
The things that actually determine long-run returns — the mental models, the process discipline, the ability to be wrong without being wrecked — take years to build and can't be bought later at any price. Start at 27 with modest capital and every mistake is tuition at a discount. The same lesson at 45, with real money on the table, costs a multiple of your net worth and lands precisely when you're too senior to admit you needed it.
So I try to treat small capital with a seriousness it won't demand on its own: writing the decisions down, sizing them deliberately, looking back honestly at the ones that worked as well as the ones that didn't. Not because the dollars require it — because the habits do, and the habits are the only part that transfers.
The money is a trailing indicator. The discipline is the asset.