Get yourself some Biotin,
I am 27 and I too noticed that my hair seemed to get thinner.
The gal that cuts my hair told me that biotin works, so I picked some up, and it made a huge difference
You can buy it at walmart for cheap. Like $6.00 for 120 capsules 5000mcg each. I take two each night before bed. I noticed a difference within 2 weeks. My hair is thick again. Make sure you goto walmart, not GNC as the crap there is expensive!