The country of origin.
It depends on the issuing authority. The US has not devalued postage stamps since 1862, which means anything issued since then can still be used for postage. Other countries have invalidated stamps as of certain dates or events. Check with you local postal authority for specifics in other countries.
That is practically impossible to answer. There are nearly 200 countries in the world, with a wide variety of postage stamps for all kinds of categories of postage. Postage has changed through that time, with new kinds of postage and all sorts of changes in stamps. Some countries did not exist in 1960 that did in 2000, and others ceased to exist during that period. To list all the prices of all of the stamps in all of those countries and their changes, would be vast. Outside of postage stamps, then there are all kinds of other stamps, like rubber stamps and metal stamps, stamps on products etc. They all have costs too that have changed. So your question has a vast list of answers, that would be impossible to give you.
If you mean stamps for items of post you are sending to other countries, yes, Australia Post has a range of Australian International postage stamps, which are marked accordingly, in blue on the edge. If you mean stamps from other countries, no, Australia Post is not a commercial outlet for the post offices of other countries. Some of the larger Post Offices may stock packets of used (or CTO) postage stamps from other countries at minimal cost. The packets are usually focussed on a specific theme such as dogs, trains, birds, etc.
You must use English/British stamps if you are posting from England or other parts of Britain
By law, United States postage stamps can honor only those individuals that have died or fictional characters. However, other nations can and do use living persons on their stamps. For example, British stamps often feature portraits of the current monarch and many stamps from Vatican City show the current Pope.
A philatelist is a person who collects stamps and can also be referred to as a lover of stamps.
I can go to my local post office! They sell Thai postage stamps. They don't sell US stamps. I think you're a little confused - you can buy stamps wherever you live to send things to any part of the world. You don't need to use British stamps to send a letter to England. You can buy other kinds of stamps from other countries, you would have to find someone that can import them. You should try finding Stamp Collectors and such. There are also commercial websites.
That is what stamps are for, to pay postage. In the US you buy postage stamps and put them on mail to any other country in the world.
Yes as long as the other stamps have not been cancelled
The letter that has the stamp of that country MUST be mailed in that country. Like anything stamp related this is not HARD and FAST. Spanish Andorra stamps can be used in Spain and certain Spanish stamps have legitimately been allowed for use in Andorra to pre pay covers internally and abroad. British Forces Post Offices in various countries through out the world (BFPO's) have also used British stamps to forward mail back to the UK therefore there as they say exceptions to every rule!
those stamps are forever stamps they will always coast the same as other stamps
There was a sheet of 33 cent baseball heros stamps that included one of Lou Gehrig. Other countries have issued stamps, St. Vincent issued one about 1992.