Trust Tim Bowen when it comes to word grammar: he has experience on his side.
The word side is normally used as a noun but can also function as an adjective or a verb.
As an adjective, it is only used pre-nominally and is found in noun phrases such as side street or side road, side dish or side order, side effect and side issue, a subject that is connected to the main subject of a discussion but is less important.
As a verb, side means to agree with one particular person or group of people and support them in an argument, as in ‘She always sides with my brother’.
As a noun, side is used in a number of idiomatic phrases. If you say that someone is on the heavy / fat / thin side or that a particular event was on the long / short side or that you will be on the late side, you are using these expressions to mean slightly heavy, long, late and so on. If you are on the right / wrong side of someone, you are indicating that they like or don’t like you respectively, but if you are on the right / wrong side of 40, 50 etc, you are either younger or older than a particular age.
If an activity is done on the side it is in addition to what is usual, as in ‘The group’s lead singer has been making solo appearances on the side’.
In informal usage, if you have a bit on the side, you are conducting a secret love affair, usually when you are already married or in a relationship.
If you have age or experience on your side, you have a particular advantage that will make it easier for you to succeed in future, as in ‘He’s lost his job but at least he has age on his side’.