Age Subgroups

[one2many]

I am trying to create a decision tree with a markov model for a diagnostic technology that addresses vague symptoms. Prevalence increases with age and I would like to create subgroups for >60 and >70 years as likelihood of missed diagnosis increases over 70. How would I add an age subgroup? This is for ED triage, so the end result is admit/accurate, admit/not accurate, not admit/not accurate, not admit/accurate. I am not sure I need to include age subgroups or should include a prevalence with age distribution.