I'll do the best I can here.
Are all the mines out there gold mines?
They primarily mined Gold. There was also a large Iron mining operation farther South (Eagle Mountain) and other products like Silver and Copper were likely being produced as well. Those commodities may not have been present in high enough concentrations to warrant mining, but it was often worth it to recover them from ores that were already taken out.
How old would you say they are on an average? Are they what would be considered newer mines or those that date back to the California Gold Rush?
The mines out there range from late 1800s and were worked during various periods for the next hundred years, depending on Gold prices and such. The last ones shut down in the late 1970s/early 1980s.
In your exploration of mines, have you seen gold or other valuables down in the shafts?
Gold ore quality is usually expressed in a quantity like ounces per ton. So it's not something you would see just looking around the tailings pile or examining the rock in the mine. I suppose you could find a nugget with a metal detector, but I've never seen that. Occasionally you'll find interesting stuff like miner's graffiti and such.
Approximately how many mines have you been in/explored?
I've lost count. I'm sure it's in the 100s.
Do you have to do many rescues from abandoned mines?
Surprisingly, no. At least until this year - our team assisted with this search/recovery and another one near the community of Red Mountain. There are occasions when I hear about someone driving an ATV or dirt bike into an unmarked shaft, but I haven't heard of that happening in a long time in San Bernardino County.