Gates did not start Microsoft with a loan from his parents, it was entirely bootstrapped financially.

Paul Allen and Gates had saved up a small amount of money from contract work. Together they provided all of Microsoft's seed capital. They had customers for Microsoft essentially from the start of the business (MITS being the first), making it profitable nearly from day one.

Which completely bypasses the point that their parents had to be wealthy enough to provide for his education at a school that had computing labs at a time that they were very rare. Bill Gates and Paul Allen certainly had to work their tails off, but negating that having a wealthy parent puts you in a far higher likelihood to be successful is just silly. The average child of poor parents is not likely to have the same opportunity as those of a child of wealthy parents. It's exactly what perpetuates the cycle of wealth.

Lots of people started microcomputer companies at about the same time as Gates. Evidently, not attending Lakeside was not a barrier.

Gary Kildall wrote CP/M in 1974, a year before Gates formed Microsoft.

$23,420.63 in todays dollars. [http://www.in2013dollars.com/1975-dollars-in-2018?amount=500...]

I.e. the price of a modest new car. Hardly "immense".

My parents bought a car for me to drive back when I was a teen. It cost $900, not $25,000.

The average price of a new car in 1975 was $4,960.

http://www.autonews.com/article/19960626/ANA/606260830/1975-...

I wrote "new" car.

What valuation do you give his mother's influence over the board at IBM?

It's unknowable. But keep in mind that Microsoft was already established and very successful at the time, and Gates was a very astute and aggressive businessman. IBM went to Digital Research first, and Gary Kildall suggested they check with Microsoft. Microsoft was the biggest player in microcomputer software at the time. Why wouldn't they check?

And how much credence would IBM give a mom (who had little knowledge of computers and software) who suggested checking out her son?

Lastly, the accounts of her advising IBM to use her son's company are not verifiable.

IBM went to Gary Kildall first.