behaviour

Question
my gelding of nearly two years old keeps on mounting another gelding when in the field together! is this normal?

Answer
This is not exactly "abnormal".  Sometimes this behavior can be an expression of dominance.  However, more likely his testosterone levels are high.  Your vet can run a test to determine if that is the case. On rare occasion it can be symptomatic of an improperly gelded horse.  I recommend you contact your vet to come take a look.