Yes you can let a juvenile apple tree mature a couple of fruits, if it
pleases you. How will you feel if animals or guests pinch the fruit?
I have a handful of mature fruit trees (apple, pear, apricot) that had
been neglected for years and were producing scant nasty tasting fruits.
After a few years of cleaning up all debris, pruning, and just a single
application of a minimal quantity of fertilizer, this year all trees
except one produced excellent fruit. The one I think is a feral recruit
from seed. It flowers well in a shady location (!), so for now I am
leaving it for its ornamental value and as a pollinator for the others.
The prunings I saved for use in a smoker and now we are enjoying fruit
wood smoked meats. Yum!
This year I planted some cherry trees. They will need pruning for shape
over the next few years. If I stay on top of it, their pruning will
consist of little more than pinching buds. It is exquisite work, kind
of like bonsai. Many minutes of contemplation, then cut in an instant.
I am considering using wire wraps, a bonsai shaping technique, on the
apples to turn some suckers into replacement limbs that grow just where
I want them.
I have a long fence now decorated with virginia creeper. I want to put
grape vines there. Probably animals will get most of the fruit, but
the fence is on a property line and the neighbors have a dog. The dog
might help guard the fruit.