I don't view age as being simply a number for one main reason: there are different types of age. There is psychological age, biological age, sociocultural age, chronological age, legal age, etc... . The one commonly used is chronological age so if you are to ask whether that type is a number, then obviously the answer is yes it is. Legal age would also be a number, such as the age for legal sex, age for being considered an adult, etc... .

However, despite your chronological age, your psychological age can be different as that is that age at which you feel you currently are. So, you can be 90-years old yet feel like you're a 20-year old ready to go. In the OP's case, your chronological age may not be matching your psychological age and that is where some confusion can arise.

Biological age is the age that if everything goes wonderfully right, it's the max. age you could live. We always like to consider the ideal circumstances for scenarios so we can compare them. Sociocultural age uses the chronological age and is what society expects you to be doing at that age. For example, if you're 90-years old chronologically, society expects to see you old, wrinkly, perhaps crippled, cognitively-impaired, your sensory systems are failing, etc... . They're not expecting to see you doing backflips and bench-pressing 500 pounds.

So at the end of this post that probably has little flow, age is not simply a number: legal and chronological ages are a number.