1) to determine how old was the athlete for each individual performances.
I have done this by using DATEDIFF function (Date of birth / date of performance). No problem so far.
2) to normalize all athlete's performances for each individual so the best time/mark is 100% or career peak performance.
The end goal is to find out what is the performance profile for a specific sport in relation with athlete's age; so if there is any correlation, I may find out that the majority of sprinters have their best performance around the age 20-25.
Hm, so you already have his Age on specific performance. You just take the min / max (depends on the discipline), for instance the min of 100m run and save his age for his best performance. Afterwards you should have a table with 2 (or 3 columns): age, best performance and discipline. I would make a scatter plot for each seperate discipline with age and best performance. You should visual see if theres any correalation..