People
I shall never be able to realise the too sanguine hopes of my friends, for at twenty-eight I am a thoroughly old man - mentally and bodily. Far more so, indeed, than I am willing to express.
— Branwell Bronte

Behind the line May contain spoilers.
Our reading
An editorial interpretation.
At twenty-eight, the speaker feels worn out in mind and body, and believes he can never fulfil the optimistic hopes his friends hold. He adds that the exhaustion is even deeper than he is willing to say, hiding the full weight of his weariness.
Context reviewed