This is a most attractive form of what is commonly known as "box elder". It's not elder, but as you know, an acer. Definitely not a sycamore. The ordinary green form can reach 35 to 40ft but this is slightly less vigorous. However, if you keep it pruned, in the winter months reducing the leaders back by two thirds (or as much as you want, allowing for it to make 2 - 3ft of growth a year), then you'll easily control it. Young growth is a very pretty shrimp pink, and the stems have a greyish 'bloom' on them which gives them an ethereal air in a winter mist. In a pot it will be far less vigorous, and may only get up to 8ft or so.

You can also trim this one back from mid July if it's got too large or if isn't a nice shape, but don't prune hard at that time of year. Also, don't prune between about February and end of June because it'll bleed like mad. I trimmed mine back a couple of weeks ago, which is a bit of a shame because the pink shading had only just appeared, prior to June, it was white and green only, mine never shows any pink before late May most years.

Worthy - whats a leader?