The best way to analyze prospects is using their age in relation to the level they are playing at. Without taking too much of the level into account to start, I'll just be looking at age. I use a players age based on the date that MLB uses to define whether a player will be a draft eligible sophomore, because much of my analysis originates with a players drafted year. If a player is 26.01 on that date, he falls into the 26 year old age category. The age won't always match what is listed on Baseball Reference or FanGraphs but that is how I do it. If I don't have a players birthdate, I use the age listed on Baseball Reference.