Hi Folks, I need some suggestions

Following are the orginal variables:

DOB and Body wt measured on 6 different dates. I need following information for further processing and analysis:

Age of individuals (In days) at those six different dates when the body wt was measured, Average body wt. at 100 days and 200 days. Now, I need to know what is the most efficient and derivative method? I use SAS and excel (not a pro though) and believe would know what you are talking, if in those platforms. 

I know, I have been abusing this resource for quite some time but I prefer Sajha than anyother online discussion forum or study groups. On top of that, I know personally a lot of people here in sajha do loads of data mining everday. :()

Thanks Guys!