Many(most?) people in real estate have absolutely no idea what they are talking about. This is an example.
Avoiding older homes because they are old isn't great advice. Avoiding homes that are falling apart is better advice (for most people, not all) but not all old homes are falling apart and not all newer homes are well built and will be falling apart in 10 years or sooner.
Most older homes (that are still standing) are well built, having been built to last, and some have been well maintained and upgraded over the years. The best quality houses I've ever lived in were over a century old. The worst quality house I've ever lived in was 40 years old and was the only "modern" house I've ever lived in and every single corner was cut building the thing.
Older homes often have some great architectural features that you can't find today, you aren't going to find a 20 year old home with an ornate hand carved mahogany staircase, for example. A lot of it comes down to personal preference and what you are used to.
The water never tastes funny.
My friends moved into a (rented) older, turn of the century, home that was poorly maintained and it's a garbage place to live. But it isn't like that's not obvious when you tour the place. My other friends bought a house built in the 1700s and it's the most well-built house I've ever seen. It has its quirks but its well-maintained and has most of the modern features you'd expect. It's also very well isolated.
Problem with newer homes, especially McMansions, is many are poor construction that aren't meant to last. They went up fast and cheap. This doesn't apply to all new construction, of course, but there was rush to build during the housing bubble. Corners were cut. Some houses were meant to look just good enough to sell, not to last a century.
Neighborhood is more important and theres not always a choice of a new home in many neighborhoods. For example, when we bought our house we had no choice but to buy old construction unless we wanted to change our neighborhood preference. Then we'd have to buy a McMansion on the outskirts of town away from everything except other McMansions. We'd be unable to walk anywhere, much further drive from work, much further drive to pretty much anywhere, and we'd have to buy double the amount of home than we'd prefer to buy.
If it's an established neighborhood you're going to get established homes!
But saying "avoid old homes" as generic advice to everyone is terrible advice. It's all tradeoffs and personal preference and also quality of the specific home. A well-built, well-maintained home is still a well-built, well-maintained home.
Most real estate agents also have zero knowledge about the mechanical/engineering aspects of a property. Whenever I ask them about the insulation, electrical wiring, HVAC, or plumbing they just give me a blank face and try to redirect me to how good the kitchen appliances and cabinets look. :(
When touring a house once I asked the seller's agent if the fireplace was functional and operational. She said "I don't live here, so I don't know." I mean, a fireplace is a main feature and some are just ornamental so you'd think she'd think to ask the sellers about it. And if she really didn't know why not answer "I'll ask the sellers and get back to you on that one." Nope, just left it at shrug. Half the times when I've toured properties I got the impression it was the first time the seller's agent had even been in the house.
Many only know how to parrot "factoids" they've heard somewhere. "Don't buy and living in 100 year old houses" is one such example. Maybe they just don't like that older homes are cheaper and they are trying to maximize their commission.
Avoiding older homes because they are old isn't great advice. Avoiding homes that are falling apart is better advice (for most people, not all) but not all old homes are falling apart and not all newer homes are well built and will be falling apart in 10 years or sooner.
Most older homes (that are still standing) are well built, having been built to last, and some have been well maintained and upgraded over the years. The best quality houses I've ever lived in were over a century old. The worst quality house I've ever lived in was 40 years old and was the only "modern" house I've ever lived in and every single corner was cut building the thing.
Older homes often have some great architectural features that you can't find today, you aren't going to find a 20 year old home with an ornate hand carved mahogany staircase, for example. A lot of it comes down to personal preference and what you are used to.
The water never tastes funny.
My friends moved into a (rented) older, turn of the century, home that was poorly maintained and it's a garbage place to live. But it isn't like that's not obvious when you tour the place. My other friends bought a house built in the 1700s and it's the most well-built house I've ever seen. It has its quirks but its well-maintained and has most of the modern features you'd expect. It's also very well isolated.
Problem with newer homes, especially McMansions, is many are poor construction that aren't meant to last. They went up fast and cheap. This doesn't apply to all new construction, of course, but there was rush to build during the housing bubble. Corners were cut. Some houses were meant to look just good enough to sell, not to last a century.
Neighborhood is more important and theres not always a choice of a new home in many neighborhoods. For example, when we bought our house we had no choice but to buy old construction unless we wanted to change our neighborhood preference. Then we'd have to buy a McMansion on the outskirts of town away from everything except other McMansions. We'd be unable to walk anywhere, much further drive from work, much further drive to pretty much anywhere, and we'd have to buy double the amount of home than we'd prefer to buy.
If it's an established neighborhood you're going to get established homes!
But saying "avoid old homes" as generic advice to everyone is terrible advice. It's all tradeoffs and personal preference and also quality of the specific home. A well-built, well-maintained home is still a well-built, well-maintained home.