The game producers have not officially established Ghost's age, as the character never openly acknowledges it. However, fans believe that Ghost is in his mid to late twenties and this is due to Ghost's Lieutenant rank in MW2. This is the average age of army troops in this rank.
Lewis features in a hero content piece in which we we see the character Ghost embarking on another dangerous mission; the twist is revealed when Ghost removes his mask and we see that Lewis Capaldi is the man behind the mask.