No, you can do it now - but do remember to keep it pruned back twice a year minimum, or it'll be 50 feet in no time...

Keep eucalptus trees away from houses and drains as the roots can give big problems as the tree gets bigger

Eucalyptus need to be kept in check as they grow fast - even in Northumberland! I have two varieties plus a junior Acacia Dealbata. Twice a year you can trim back the folige - it doesn't seem to upset them, they keep coming back so, just keep it to the size you want unless you want a fifty foot Eucalyptus arguing with your neighbors!

I agree, mine had to come down because they got away from me I was also told they are prone to blowing over too when that tall.

I've heard that rumour on this site before, Drc, but have found it to be completely untrue - Eucalyptus is one of the deepest rooting trees in the world, so the only time it might blow over is if its planted in very shallow soil, possibly over bedrock.
And Pam, your tree should be a minimum of 40 feet away from yours, and anyone else's, house.

That does surprise me Bamboo we were told this by a 2 different tree surgeons when I had both my gunni taken down. Still mine had to come down anyway.

when I was doing my training, Eucalyptus gunni, we were told was, in fact, the deepest rooting tree in the world - I'm not convinced, personally, I think its more likely to be Sequoia, but who am I to argue! On the other hand, I'm more inclined to believe the RHS lecturer than a tree surgeon, if I had to choose.

Please be aware there are many varieties of Eucalyptus, the gunni being the most common in the UK. I have a eucalyptus niphophila (snow gum)which is a much smaller variety and only grows to 20 ft. The bark is much nicer and the leaves are larger, very pretty and shouldn't cause many problems with neighbours.
Here is a link to the different varieties

http://www.desert-tropicals.com/Plants/Myrtaceae/Eucalyptus.html

And because gunni is the most common in Britain, I assumed that's what Pam was talking about, Andrea.

Not trying critisise, just trying to provide some useful information to the person asking the question.

Sorry if that sounded snippy, didn't mean to, Andrea, and I didn't take what you said as criticism - was really trying to point out to Pam that my advice was based on the assumption it was gunni;-))