Aces High II, or any good flight simulator, is always going to heat the CPU and video card GPU up more than other software. It is due to the extreme amount of floating point math required to handle flight simulation.
It is not unusual for CPU's to progressively get hotter and hotter with age. The primary reason is the contact between the CPU and the heat sink. Overtime, the thermal pad/paste loses its ability to flow correctly, esssentially drying out and causing progressively worse thermal transfer from the CPU to the heat sink.
Removing the heat sink and thorouhgly cleaning the CPU and heat sink contact area (isopropyl alcohol is good for most instances), then applying a fresh coat of quality thermal paste will normally restore the performance of the heat sink.
The above is pretty general. There could be a lot of other things, such as clogged air intakes on the case, fans not rotating as fast as they used to (they will do this as they age), and so on.
