Trying to get my 14 year old son a solid bike for riding around and got my eyes on a used 2011 Trek Navigator 3.0.

Problem is the bike is 40 miles away and I don't want to make a trip if it's not the right size.

My son is 5'5" tall with an inseam of 29".

The seller says the Trek bike is of 18.5" in size. I asked if this is a frame size and he said probably but not sure.

I looked up the bike's specs, could find 3.0 specs but found 2.0 specs, assuming they are the same geometry (are they?) It says:

The Trek Navigator 2.0 comes in four sizes, with frames measuring 14.5, 16.5, 18 and 21 inches. The frame of the bike is made from Alpha White Aluminum. The bicycle is built with a 50 mm RST Neon T front suspension with Clix dropouts.
The wheelbases of the XS, S, M and L models measure 40.1, 40.7, 41.0 and 42.1 inches, respectively. The trail is 2.9 inches long, while the head angle measures 69.0 degrees and the seat angle stands at 68 degrees for all sizes. The chainstay is 17.1 inches long. The effective top tube measures 22.2, 22.8, 23.1 and 24.2 inches for the XS, S, M and L sizes. The bike also features an 11.1-inch bottom bracket and a 2.0-inch offset.


Another site says the 3.0 has sizes "14.5, 16.5, 18.5, 21"

An 18.5" frame size with an 11.1" bottom bracket will end up with the seat post insert point being 29.6" above ground, and is too high for someone with an inseam of 29" right?