887
Don't grow older than 255 or else it will overflow
(feddit.org)
A photo of a cake with 8 candles in a row. The first and fifth candle from the right are lit. The caption reads "Happy 17th Birthday"
How about 4294967295?
with 8 bit?
64 bits and you get to watch heat death slowly set in. (Or, y'know, cosmological catastrophe depending on the full physics)