Rob, it is evident just from the appearance, and quick distinguishing between a hard, semi hard and soft bull comes with experience, so imperative to trust your experienced PH. Unless I misunderstood, I don't agree with what LvW said regarding the height of the tips. Sure, the tips of a Buff will drop with age, but it is not the sole distinguishing factor to age a Buff. The height of the tips has more to do with genes. Some Buffalo will never drop to bellow their bosses, no matter how old they are. I speak under correction, but I believe the Addo bloodline is known for that.
A Buffalo will also harden from the outside, back, towards the inside front. So, it is possible for a Buffalo bull to look hard from the back, but still soft in the front.
It always makes me more comfortable to see a Buff from the front, to be entirely sure, before taking the shot. If one does not have that luxury, and the Buff looks hard, at least from the side, the next thing you should be looking for is the Roman nose, which is only evident in older bulls, as well as the small dewlap that develops on these aged bulls.

) which has all the things I would look for in a good trophy if I had such luxury of choice. Hard, solid bosses, tips slightly laid out and not poking up above bosses, bosses with good rough character, obvious "fattening' of horn cross section at bottom of sweep and a wide, flat top appearance to the bosses when viewed head on. It is one outstanding bull!, IMO.
Hunting the Save a few years back, shots presented themselves after hunting hard for several days, and I had to make a quick decision between a 42" smooth, smaller bossed younger bull or a 37.9999" nice, gnarly-bossed and horned, deeper-curl daggaboy covered in mud (We'd seen him running away from us in the shadows a couple times earlier). He was clearly older and had more character (also the right one to take out.) That said, a couple days later (on the last eve,) my son got the 42"er. All's well that ends well...He kept his as a Euro mount due to his rather excellent (frontal) shot...The late Phil Smythe was fussy about the buffalo he chose for his client's to shoot, the width was just what came, the first criterion had to be an attractive boss and horns. A good bull just looks right.