prepare a starter is to combine about 4 cups of water with 1 cup of DME, boil for 10-15 minutes and cool to pitching temp.

Well, I followed his advice to the letter but my starter isn't doing a hell of a lot!

4 cups of water plus 1 cup of DME gave your starter wort a original gravity of 1.120

BEFORE you boiled it.

Boiling removed water and increased the original gravity of the starter wort even higher.

I suspect your starter yeast is suffering from high gravity shock.

What numbers are you using to calculate this? Working backwards, it looks like you're estimating a cup of DME to weight 11 oz or the water volume is off by half. Granulated sugar is closer to 7 oz, in my experience a cup of DME is less, about 5.5 - 6 oz (there's variability). I figure this starter would be about 1.065 pre-boil, more after. It's still too high though. A half cup of DME in a quart would be better for the starter.

But weighing is better than volume measurements, I use DME equaling 8-10% of the water weight.

Pre-boil Specific Gravity calculations:

Densities measured at STP

Water has a density of 1.000 g/mL

DME has a density of 1.6 g/mL

1 cup = 8 fluid oz.

1 fluid ounce = 29.57 mL

1 cup DME = 1cup x 8oz/cup x 29.57mL/oz x 1.6g/mL = 378.5g DME

4 cups water = 4cup x 8oz/cup x 29.57mL/oz x 1.0g/mL = 946.2g water

5 cups solution = 378.5g DME + 946.2g water = 1324.7g wort

5 cups solution = 5 cups x 8oz/cup x 29.57mL/oz = 1182.8 mL wort

Density = 1324.7g / 1182.8mL = 1.120g/mL

Specific Gravity = (1.120g/mL) / (1.000g/mL) = 1.120