To make things more clear I checked the birthdates.
Bella - xx/xx/1948
Andi - xx/xx/1954
Cissa - xx/xx/1960
These are the new uniform years so every Marauder should have a 1960 birthdate (granted even with that some have not had their birthday yet) making them late teens/early 20s.
All those who are Lucius/Andi's age should be in their mid-20s.
All the older ones like Bella/Arthur/Molly should be in their early-30s.
Thank you for your understanding.