introduce the cat to the garden for about an half hour a day, keep an eye on him, he will be a bit nervous at first, make sure there are no dangerous roads in the area, as i wouldnt recommend letting him out if this is the case.
Cats are very intelligent, i have 8 cats, i do find that cats love being outside more than being inside but do bear in mind more accidents can happen outside in the wild,i have found that i have been so worried in the past when they go out, my first cat i got a lead and i took him out each day on the lead in the garden, and one day he got under the fence the lead came off, and i was calling and calling him, crying my eyes out and panicking, then about 20 mins later he popped his head up from the end of the fence, and ran away again, evenually after around an hour, he decided he would come close enough for me to return him back to safety but he loved it.
A good tip is let the cat out before you feed him, and you can call him in, for food, as a fed cat is a happy cat so you will never get him back in, if you feed him before he goes out.
The whole training process is very quick but just introduce him to the garden a bit at first, as sometimes they do get into trouble and end up too high in trees or in my cats case on top of a garden shed,2 doors down and the people were out at the time and he cried and cried and i kept calling him, and all of a sudden there was thunder and lightening and a huge downpour and he came down so quick so they do learn very quick and the answer to your qustion is yes he would be ready for summer, and they would know how to come back there is also an old wifes tale that if you put a little bit of butter on the cats paws he will follow the scent back home but they are really clever and they do come back when they want to(of course), a cat flap is a great idea too as otherwise you find you are opening the door and closing it all day,as they can neer make up their minds if they want to come in or go out, but with a cat flap he can come and go as he pleases and hope this helps.