How old is Moe on 'The Simpsons'?

This is the closest you will get to finding out his age. He was a child actor with Our Gang in the 1940's.

https://simpsons.fandom.com/wiki/Moe_Szyslak

I don't think his age has ever been specified. However, we do know that he was one of the "Little Rascals" or "Our Gang". These were made between 1922 and 1944. Moe appeared in the Simpsons when it started in 1989 and of course, none of the characters have aged since then. This would put him at anything between 55 and 77.

https://en.wikipedia.org/wiki/The_Little_Rascals

Just to add, that was assuming an age of 10 when he appeared in Our Gang.

He claims to be one of the original Little Rascals, and later became a boxer before establishing Moe's. He was also abandoned by his parents at a camp that Homer attended as a boy of ten. This raises some dispute as to his age--is he in his late thirties to early forties like Homer Simpson or around eighty, like Charles Montgomery Burns?

Morris "Moe" Szyslak is a character voiced by Christopher Collins, Now Hank Azaria.

Gender: Male
Hair: Curly and Black, later Gray
Age: 45
Job: Owner and proprietor of Moe's Tavern

http://simpsons.wikia.com/wiki/Moe_Szyslak