In reply to rockjedi12345:
If you are not setting yourself an ambitious time and have a reasonable baseline fitness a half marathon is doable without any further training.
You can just think of it as two of your regular training runs. Take some speed off the first, so you get through your second.
I didn´t run for ages either (but do longish hikes and cycle to work), and recently just ran something like 28km in a charity race (point to point, hence the weird distance).
CB
PS: I am 47 yo and weigh about 100kg