Medieval warfare

by OwainWill01

This will be a collection of questions about gaps in my knowledge of medieval warfare (specifically western European warfare in the high and late middle ages)

1)Who made up the bulk of an army? 2)Did the bulk of the army willingly join or were they conscripted? 3)What was the rough age range between soldiers in the army? 4)How would non-noble soldiers show their allegiance? Would they wear the arms of their lord or their king? 5)Would non-noble soldiers be given any equipment by their lord?
6)When soldiers are depicted as having arms on their shields, would they paint this on themselves or be given the shield? 7)How did mercenaries show their allegiance? 8)Could a noble have nearly anything on their arms? As in, we're they allowed to put whatever charges they wanted to on their arms?

I may have more questions later, but that's all for now.

I don't usually do this, but I'll try to do this in list form so that it lines up with your questions.

1-2) By the late 11th and early 12th century, western European armies had almost entirely abandoned the general levy of all freemen. Aristocrats were still prone to being summoned to war, but that system would itself collapse in the late 13th century. Conscription is not a concept known during the Middle Ages. The army could be gathered in a variety of ways: aristocrats fulfilling their obligations; retinue men belonging to the households of the king or various aristocrats; men hired for the campaign on an individual basis; companies of mercenaries (especially after about 1150). In general, paid service became more common throughout the Middle Ages. The bulk of the army would generally be infantry of some stripe, some of whom rode to battle (mounted infantry). Likewise, while knights are often called cavalrymen, the truth is that they were rather more like dragoons; they rode to battle but dismounted as often as they fought from horseback.

It could vary tremendously. We absolutely know that some knights and lords actively fought into their sixties and seventies. A general range would probably be 20-45, but that's largely a guess.
We don't really have evidence for this until later in the period than I'm fully comfortable talking about. By the 14th century lords had started equipping their retinues with matching clothes based on their own colors, and during the Hundred Years War the English soldiers generally sewed St George crosses on their clothing. In general, though, you know who your own guys are because they're standing next to you in formation, and the enemy's soldiers are facing you in their formation.
Yes, certainly. It was a lord's responsibility to ensure that the soldiers of his household were properly equipped for war. If they showed up to a muster poorly armed, it would not only reflect badly on the lord, it might get him killed.

As an addendum, knights don't really become synonymous with nobility until the end of the 12th century. So prior to that point, the vast majority of soldiers in an army would be non-noble.

We don't know.
We don't know if, or how, they did. Given that medieval armies rarely topped 10,000 men, it's just not that hard to keep track of who's who.
I'm far from an expert on heraldry, but it's my understanding that prior to the 14th century, arms were much less formal or regulated. After that point, it became important that one's arms be unique and identifiable.