What really is the best way to start?

[Foxstro]

I'm 18, tall and thin all in good health and fair fitness.

I'm looking to incorporate road riding into my fitness plan on the days I'm not down the gym, I just don't know how to start.

I rarely do much work on Cardio so this is really needed.

Is it best to aim for a time, distance, speed? And what is reasonable for a beginner to achieve?

 

[T.M.H.N.E.T]

There is a time and a place for specific time,speed and distance training. You need to decide what and how those fit into your goals.

 

[lulubel]

Just get on your bike and ride at a speed you're comfortable with until you run out of time/get tired/feel ready to go home.

That will give you much more idea of what you're capable of at the moment than anything we say here.

Don't over-complicate it

 

[Norm]

Just get on your bike and ride at a speed you're comfortable with until you run out of time/get tired/feel ready to go home.

^^This^^ IMO.

The best way to start is just to get on with it and not be too worried about the longer term goals. Those will come, given time, but get some time on the bike to get used to the different requirements that cycling puts on you and, ultimately, to give yourself a sound base line for future reference.