If you want to support "10+ year old" cards (such as NV30/Geforce FX, or R300/Radeon-9000), you are stuck with OpenGL 2, yes. Though all cards that can support 2.0 can support 2.1 as well (presumed that the driver is up-to-date). This adds pixel buffer object functionality, which may be interesting if you have a lot of sprites to upload for your 2D game.
I would personally never touch anything less than OpenGL 3 again in my life, which is supported by 9 year old graphics cards (such as Geforce 8). The reason not being that the additional hardware functionality is that much useful in comparison, but simply that OpenGL 2.0 is a nightmare to get going with three dozen extensions that you need for some of the most basic things, and no sane guarantees on texture sizes and such. Almost every graphics card, even 15-16 year old ones, can do more than the bare minimum, but given no minimum guarantees you don't know for sure unless you spend considerable work querying (you can't even be sure that you can use a 512-texture).
OpenGL 3 on the other hand, comes with sane (not great, but OK) minimum guarantees and provides almost all functionality that you need, for 90% of everything you will ever be doing in your life (for the other 10% you'll need GL4).