A landlord can charge for excessive wear and tear on carpet only if it's unreasonable wear and tear. After five years, according to national standards, a carpet is deemed to be completely worn, and such wear is considered reasonable. So in answer to your question, the newer the carpet, the more the landlord can charge if the carpet is damaged, if it is damaged outside the reasonable wear-and-tear limits.
No, there is no requirements to replace carpet, ever, as long as it doesn't pose a health issue.
The landlord can never charge for normal wear and tear. If the carpet is unfit for further use after 4 years, that's abuse, not normal wear and tear. If, however they just show their age, you cannot be charged, your duty is to have it cleaned, that's it. A landlord is only obliged to replace carpet that is no longer fit for use and that is not tied to any number of years, it is all about the condition.
The landlord's duty is to keep a property "habitable" - fit to live in. If the carpet is well worn and hopelessly filthy-looking, a city official may decide it must be replaced. If there are no holes and discoloration is limited to high-traffic areas, then it would probably not be considered too bad. Also, a landlord will replace the carpet if it helps him rent it quicker or for more money. If he's not replacing it, the reason is probably because the tenant is getting a good deal or just unwilling to look for a better place.
It really depends on the age and condition of the carpet. Seven years is about average, but good carpets can last 15.
If there is a provision on the lease which requires that your carpet be cleaned six months prior to the expiration of the lease, then the landlord has the right to enforce those provisions. Additionally, if the carpet is damaged or dirty because of obvious abuse by the tenant and not the cause of normal wear and tear on the carpet, the landlord has the right to demand that the carpet be cleaned. However, if the carpet was not brand-new, then whatever dirt or damage occurred to it is measured according to wear and tear by the age of the carpet. Carpeting of five years of age or older is usually deemed to have reached its maximum age, for which the landlord has no claim. Finally, the landlord may not keep your entire security deposit simply because you didn't clean the carpet: he can only deduct the cost of cleaning the carpet from the security deposit. I doubt that your landlord can evict you simply because your carpet is dirty. If you have only been in your apartment for six months and your landlord evicts you because the carpet is dirty, then I would take pictures and present them to court to fight your landlord.
I always thought it was down to the landlords discretion, unless it was stipulated in the lease when you signed it that it was done every ten years? Most leases probably state that any fixtures/fittings/carpet wear are down to the tenant? I guess that is what you pay a deposit for? if after 7 years the carpets are worn out the landlord can either make you pay or take it out of your deposit?
If you want to get your cleaning deposit back, clean everything thoroughly, including the carpet, and make sure the landlord knows so he or she can inspect it.
The average American home replace their carpets every 8 to 10 years.
Probably only if the carpets are old (seven years is average). Your allergies probably isn't the landlord's fault. You might want to move to a place with hardwood floors, and he might be wise to let you go.
Depending on the wear, tear, your carpet cleaning methods, and it's warranty, carpet should last aproximately 5 to 7 years.
Under California guidelines, the normal life expectancy of a carpet is 8-10 years.