fix AgeOfOldestJob when no jobs
fix AgeOfOldestJob when no jobs

mwest1066/PrairieLearn,tbretl/PrairieLearn,parasgithub/PrairieLearn,parasgithub/PrairieLearn,parasgithub/PrairieLearn,mwest1066/PrairieLearn,tbretl/PrairieLearn,rbessick5/PrairieLearn,mwest1066/PrairieLearn,parasgithub/PrairieLearn,tbretl/PrairieLearn,mwest1066/PrairieLearn,mwest1066/PrairieLearn,parasgithub/PrairieLearn,tbretl/PrairieLearn,rbessick5/PrairieLearn,rbessick5/PrairieLearn,tbretl/PrairieLearn,rbessick5/PrairieLearn,rbessick5/PrairieLearn