[SmellTheGlove]

I agree with you in principle, but 30 years is probably the wrong number. I have a house in coastal Maine, built in 1997. It's coming up on 30 years. I assure you, it's vastly different than the my first house (1941) or my last (1953), in good ways.

But to your point, we consider way too much to be "historic" and I'd like for that to change. You really should be able to tear down almost anything you'd like and rebuild as long as it's to code/zoning, and zoning needs to be cut back to things like dimensions and use, not appearance. Being old shouldn't make something eligible for historic preservation on its own.

[bluGill]

Code should be about fire safety for the fire department if it burns. if you can't build on the lot then it needs to be because of something there - or if they are planning to build it (a new utility) then they need to rebuy the easement every 10 years until they do. Height is limited only by airport flight lines.

everything else is none of your business. (Okay, I might have missed something but it is on those lines)

[cryptonector]

Height (number of units, really) is limited mainly by the bandwidth of the roads, water mains, and sewers in the area. These are things that are expensive, very expensive to expand. Of course in practice height is firstly limited by zoning to protect existing properties' owners, but you can't ignore the infrastructure needed for larger buildings.

[garciansmith]

In the United States something simply being old in no way makes it historic in any legal sense (e.g., contributing to a local historic district): integrity[1] matters if you are trying to legally deem a resource historic and worthy of some sort of preservation effort. Generally speaking buildings, structures, or objects need to be at least 50 years old, integrity aside (but there are exceptions if they are particularly noteworthy).

I tend to disagree with the need to tear stuff down just because it's old: it's so terribly wasteful. We need to get better at adapting, reusing, and adding on to older buildings. Granted, when developers just want to use the cheapest materials possible and build something that will start to have serious problems in 20 years, it's a problem, to say nothing of the loss of serious knowledge in various skilled trades.

[1] In most cases the National Register of Historic Places aspects of integrity are used for evaluation: integrity of location, design, setting, materials, workmanship, feeling, and association.