Antler points and years don't necessarily match up. So you really can't say when a buck is 2.5 years old, he will have more points when he is older. Some will, some won't. He will most likely grow more inches of antler, but those inches will not necessarily translate to additional points.
Too many things come in to play to generalize antler growth - food, age, genetics. If you have a drought in Texas over the next couple of years, those 2.5 year olds might put on very few additional inches. If you have a great year, food wise, and the deer has great genetics, those deer may add a whole lot of inches.
Just too many things come in to play to make a generalized statement.
“There are two spiritual dangers in not owning a farm. One is the danger of supposing that breakfast comes from the grocery, and the other that heat comes from the furnace.”