How to thicken hair that was always thin/light?

Apologies for starting a new thread with a similar topic to so many others but I feel my situation might be a little different. I'm a 24 year old guy with blonde/fair-ish hair that has always been thin. I don't believe I'm balding as I can see no noticeable hair loss anywhere around my head. I just remember my hair being very thin ever time the barber has wet it to cut it.
I'm always a little shocked by my thin hair when I have to look at myself in the mirror of a barber shop, but today made up my mind on wanting to get something done to help the situation, when the barber himself commented on how light my hair was.

Needless to say I wasn't overly impressed as I sat there with five or six other customers listening in to what he had to say.

But given that I'm not balding, I rarely use gels/waxes and I wash the hair ever other day with a good shampoo, what could I do to improve the condition of my light hair?