Seed-grown? Grafted? or from a cutting?

To be honest, I am not sure. 2 years old, got at a local nursery. I think seed, had thorns on branch up to about 4 feet.

Lots (which is not to say many, most, or all) are grafted, so look for the graft line if you can find it. Anything growing from under the graft line should simply be removed. Lemons do have thorns.

Technically you can remove whatever you like at any time except when the lemon's flowering or fruiting (it removes energy from the plant at that time, which you don't want), although I tend to avoid heavy pruning during winter when I can on everything I can. Here, it's out of shape enough that I'd just do it.

https://homeguides.sfgate.com/grow-pohutukawa-74987.html

The link title is a bit off-putting but it talks first about lemons. In your case, I'd probably just neaten things a little and leave most of the height, really. It's a young lemon, it's going to grow. If you'd rather impose a bushier, shorter shape, though, that's certainly fine as long as it's not too forced.