@Alucard:
1. Yes, that's perfectly fine.
2. It depends on how long you have had the endowments and how many you have. Without any endowments of metabolism a person just ages normally. With 1, they age twices as fast, with 2, three times as fast, and so on. It also depends on how long you have had them too.
My characters real age and physical age aren't too far apart because he hasn't had his endowment of metabolism for very long and only has 1. Up to 6-7 endowments of metabolism and you should be still alright though you will be aging pretty fast. Past 8-10 endowments of metabolism and its getting pretty dangerous; but hey, you'll be living life in the fast lane ^^.
@Dia (Mind if I call you Dia?):
I'm not completely sure what you mean but I am assuming you mean "roll" as in dice to get the numbers (for endowments I'm guessing)? If that is the case then you don't really "roll" to get the numbers; unless of course you just want to.
Really using the endowments is all about balance of strengths and weaknesses. Example: If you have 5 endowments of Brawn and only 1 of Stamina, then you will seriously hurt yourself if you ever use more strength than normal. Having 5 endowments of Brawn and 3-5 endowments of Stamina will counter that danger though. Another example: You have 4-5 endowments of Metabolism and only 1 of Grace; then you will be pretty fast but your body won't be able to naturally control that speed so it gets dangerous once again.
There is an explanation to all the endowments and how they work in the introductory post. If you have anymore questions though let me know, I'm glad to answer them ^^