It could be a few things. There might be something partially clogging the drain(i.e. toothbrush, a cap to a hair spray can, pop-stick...). if this is not the case then you might have a calcium problem with the p-trap or syphon-jet. If your syphon-jet is clogged up, try to break some of the calcium out of the way so you can feel water flow through it when it is flushed. The syphon-jet it typically located at the bottom of the bowl. It basically makes the toilet flush. Without the jet your toilet should not flush unless it is located "in" the p-trap.
Age isn't reason for toilet not flushing. Several things could be wrong for toilet not flushing.
The main drain is plugged. You may need to remove the toilet and snake directly down the drain.
Probably, yes because my toilet is making that sound ALL the time when you flush it.
Linkage going to flapper is sticking or needs adjusted. Nut holding flush handle to tank may need tightened or replaced. Pressure assisted toilet needs more force on handle to flush.
The toilet itself is plugged or the pipe from the toilet to the drain is plugged. It may be that the tub and sink have their own drain pipe that may connect to the main away from the toilet drain. Plunge the toilet or sometimes if you fill a 5 gallon bucket with water and pour it into the toilet as fast as it will take it, that will flush out the line. It is a greater amount of water all at once an forces out what the clog is.
There may be something that is partially blocking the drain.
look in the tank and see if the flapper is working when turning the handle or then use a plunger or buy a toilet snake they are cheap. If you have kids or etc then maybe something jammed in the trap and if you can't get it out then take out the toilet and snake it backwards. If your toilet don't flush but the drains of other fixtures work fine then its something wrong with your toilet most cases. More information is actually needed to give a proper answer
If it's leaking between the toilet and the floor, you put the wax ring in wrong. If it's leaking between the toilet and the tank, you need to replace the gasket.
Either the toilet is plugged or the sewer line under the toilet is plugged. At this point I would suggest calling in an expert (plumber) to determine the problem. You have not given enough information to say. Sounds like you do not have enough water pressure coming in to wash the waste away. Check out the holes under the lip of the toilet seat to see if they are blocked, causing you to get an inefficient flush. Our new toilet is much better at flushing with lesser amounts of water.
* Could be a clocced pipe, so that when you flush sewage backs up somewhere and you smell the odor. * Possible leak at wax seal. improperly vented or if you have a fixture that isn't being used the trap may be dry. pour water in sinks, tubs, showers.
That depends on what is wrong with it.
Generally the double flush will happen after the flapper or other internal components of the tank get replaced, it is caused by the installation of an incorrect flapper, even though some flappers do not have it noted on the packaging, there are usually 2 types of flappers, one for 1.6 gallon flush toilets and one for 3.5 gallon flush toilets. Installing the wrong flapper will cause a double flush because the flapper does not close at the correct time during the flush cycle. To correct this you will need to get a correct flapper. There is a company that makes an adjustable flapper that works on either type, it is red and has a plastic frame with a red rubber flapper that can be rotated in the fame to adjust it to your specific toilet, if you aren't sure which one you need the adjustable one may be your best option.