Getting marks when hitting milestones in growth

I think it could be a great way to encourage people to keep growing their creature (though unsure would one even need encouragement like that?). Maybe you could get 1000 marks when hitting fully adult, and/or getting bit less marks for hitting certain milestones like sub-adult like getting 400ish marks for reaching it. Or, it could be a passive quest, where if you hit juvenile for example in 2 hours time, you get little more marks or certain amount of them.