Great question. See the these pages for details:
https://docs.stsim.net/reference/prop_prob_transitions.html#age-reset-optional
https://docs.stsim.net/reference/prop_prob_transitions.html#age-shift-optional
Basically, If Age Reset is set to ‘Yes’ then the age of the simulation cell is reset to the minimum age of the destination state class after a transition occurs. In your case, that would be 41 years. If Age Reset is set to ‘No’ then the age will be set to the nearest value to the current age of the cell that still satisfies the age constraints of the destination state class. In your case, the age would be set to 70 years. Note that you could use Age Reset in combination with Age Shift. For example if you set Age Reset to ‘No’ and Age Shift to -40 a cell that was age 90 before the transition would be Age 50 after the transition. If you set Age Reset to ‘Yes’ and Age Shift to 10, a cell that was any age before the transition would be 51 (41+10) after the transition.