Yeah, I'd definitely say that having the dog for only 7 weeks would be a huge factor in his non-recall ability. Also did his last owner ever train him to come???? If that was a problem then, it wouldn't change for you now.
A suggestion would be to start over as if he's a puppy. You need to find out how his behavior is for the rest of the basic commands. Figure out what works as his motivator-- if you're rewarding him with a toy, tidbit, praise, etc... 15-20 minutes per session maybe 2x a day is enough. Always end on a positive note. Watch that he isn't losing attn. or getting tired and stop before he starts acting up.
Work with him on a six foot training leash and collar (correctly fitting) where you have complete control over him. Start with "Sits", "Down', "Stay" "Heel" and build up your time. When he can "Stay" for a couple of minutes without any reminders or corrections, walk to the end of the leash and call him to you. Use the leash to make sure he comes right too you.
After some time (days, weeks, months -- not minutes) get yourself a Lunge line (like horses use.) Then you can work him up to 20-40 feet away and still control that he will come to you. Don't use a flexi-lead.
If you decide -- "hey, he came to me once or twice, he's reliable", and let him off the leash to find out he isn't returning, you have given him more reinforcement that he is "Free" and can do this. If you let him offleash before he is trained, don't use the same command over and over to try to get him back. You are teaching him that you are helpless to make him return. So it is best that you work with him repeatedly before you let him off again.
BTW, don't forget that dogs can smell a bitch in season miles away... his attention, esp. when young can easily be distracted by this.
good luck,
toodles