If he can get that close then I'm sure he will achieve that milestone. It seems impossible for me too, but I have my own targets. At my age I can expect to get slower so I need to do what I can to improve. I did a decent 5km for me at parkrun today and that was partly down to not setting off too quickly. I have done that plenty of times before, but held back a bit this time. It was still hard at the end and I could not have done much better. This is on a trail course so I could probably be quicker on a better surface. There are so many variable though such as diet, how well you slept, recovery from previous runs and even the weather. One advantage of parkrun is that you get this weekly time trial to check your progress. There is always next week...