Assuming it's UK stuff and two rail type (real early stuff was 3 rail) you can normally tell age by the branding, Hornby Dublo before 63, 64-72 Triang Hornby and 72 onwards Hornby Railways. Early engines and rolling stock were die cast or tin pate but by mid 60s nearly everything was plastic. As with everything condition is everything and values range from next to nothing upwards depending on condition and rarity. What do you actually have?
I still have all my old train stuff in the loft, keep saying one day I will build a proper layout but actually am being encouraged by a Lancia owner here who is in to model railways in a big way. On the retirement list