USUALLY a globular cluster is reasonably easy to identify by looking at their HR diagram. GC's typically fall within the ages of 8-12.5 billion years old but there are some younger ones.
Take R136, the centre of NGC 2070 as an example. It is currently an open cluster and large nebulise region which from memory is maybe 10 million years old? Would have to double check that when not on my phone
R136 is an interesting region as it is widely accepted that in time, it will become a GC. On a cosmic scale, new born GCs are a rare event in this time of the universe. For the most part there just isn't enough molecular star clouds around to form a GC, the universe has just changed a lot over the last 5-8 billion years
From memory, R136 is currently going through its first of probably two stellar populations; most GCs have at least two and sometimes three populations.