He made General when he had a residual service of 4 years. In Pakistan, you need to have a residual service of 3 years at minimum to become General before you retire at 60. Meaning, you can become a General only when you are below 57.
So he's supposed to retire next year, 1.5 years to go. But with a 3-year extension looks like they are ignoring the retirement age. My take is it looks like the 3-year extension is up and over the remaining 1.5 years in service, so we may have to see him around for 4.5 more years.
What this means is he either intends to stay in power, or there's no one better to replace him.