You are driving a bus. At the first stop, you pick up 12 monkeys and 18 gorillas. At the second stop a giraffe and two tigers get on the bus and sit in the back. At the third stop, a zebra and pig get on and sit in the back next to the giraffe and tigers. At the last stop, an orangutan, a parrot and 27 alligators get on the bus. Then, they go to the zoo.

Now, how old is the bus driver?