It is hard to date a piece when it's not even clear what it is.
It's not 'ancient'. It sure doesn't look like a Qin seal at all, and I am not even sure it is a seal.
I can see it isn't perhaps 'new' since it has a touch of green patina.
If is was (allegedly) found in the 1800's then it may date to near the 1800's.
There should be a little more to the story of where it came from than the above if it was 'found' and kept for so long, and if that is all that you know then there is the possibilty that even that story is a later embelishment, and you should consider this option.
In this I mean the story behind the item is something you could consider dating too. Did grandma talk about it being from her parents or did somebody tell you this story 15 years ago?
Bear in mind, all the seals I have seen from the Han period (with a real signifigance to the animals atop them) and even this link above to the 19th century versions of seal make a basically square impression when the ink is put on paper, and the figures above them are symetrical and balanced (i.e dragons or tortoises etc).
It is therefore not going to be an official seal.
If it is a stamp at all are the characters
reversed? Have you stamped it and translated it?
In 15 years you should have found somebody to translate it. Chinese script is a continuity.
My wife can read some ancient characters, and I am sure even if it a Zhou-era script it could be read (as in I have a few people I could try). The style of the writing is not a way to date an item by itself by the way. It is just like a persons hand writing, and modern people put these on items too.
If you want it translated you could try Stephen Selby at ATARN, who can read ancient scripts and has done this before. Search for ATARN on the web and send him a question.
I have a friend in Taiwan who could try too, but he doesn't speak English so it is complex.
Surely somebody on CHF or an educated Chinese with a good knowledge of traditonal characters could work it out?
I will leave that to somebody else.
My opinion? translate the characters, figure out if it is reversed. Even if that means only translating one character you will get your answer. That at least rules out the stamp idea if you do.
I think it basically looks like a toy or a figurine basically.
This doesn't mean it can't be 200 years old, or from the Ching period but keep open the possiblity it is from a Chinese version of Kinder Surprise.
Such a humaniod-animal creature may relate to a folk story or character in China.
There are several avenues to try and find info from.
The base is very much like a toy soldier and not like a seal. I assume it is small? These plastic soldiers are here only to show the shape of the base they stand upon, and therefore suggest the bronze/brass item you have is a figurine too.

This Thai lady here makes bronze figurines today, you could send her a picture and see if she knows what it is.
http://www.bronze-sculpture.net/bronze-his...ax-process.htmlOne of hers is attached below.