Quit shooting 1.5 year old bucks? haha but seriously though, I feel like where I hunt the jump in antler growth between 1.5 and 2.5 years old is so big that it is hard to distinguish which bucks are what.
I think that's fairly standard. Most bucks will stick around their mother that first year. They will get kicked away during the rut, but they generally catch back up with her during the late season. They will hang around the same area they grew up, but when they start to get the itch to breed, they will usually move out of their area. I think it is mother natures way to keep down any inbreeding with their mothers or sisters.
My neighbors shot a fawn with spots to say they got a deer. So kinda but not really with bucks. They just shoot what they first see. As for a solution I can't think of one besides just try to ask the neighbors to shoot older deer which is impossible for me.
It's nature, no way of preventing it. Improve your habitat and hopefully you can draw bucks dispersed from other properties.
I don't think the 1.5 year olds want to compete with the 4.5 to 5.5 year olds during rut so they move on to a new area. I wouldn't be surprised if some of your 1.5 year olds from 3 years ago are your hitlist deer now.
The good news is that if you have quality habitat. Food, water and cover, yearling bucks will move into your property.
If you're saying you have no 2.5 y.o. bucks on your property, its b/c people are prescribing to the "once a spike, always a spike" theory. Yearling disbursal not only affects your property (losing them) but your neighbors too, so in reality there should be little net loss if you have the proper habitat to keep a buck. We stopped shooting anything younger than approx 3.5 and the number of shooter bucks has soared.
