dull time? yo lo traduciría como tiempo aburrido.

but if it said : what dull time it was......it would be 'soso´?

<<su juventud!>> No, if that were the case, it would say: ... qué sosA era!

It is very clear because when “soso” is used in this way in Spanish, it refers to the person, in this case, “I”.

how can one tell the difference here between 'it' or 'he'' or ''I'????

no, él, su persona.

su juventud!

... how dull I was! ??