DS banged my pots and pans with passion when he was a tot. At one, we gave him a toy snare drum, and added that to the drum set I'd made out of my giant Christmas tins (the kind popcorn comes in). At 1 1/2, he watched us rehearse (DH and I are in a band) and was mesmermized by our drummer who was nice enough to let him sit and play on the big kit. Tearing him away was nearly impossible. After much thought about buying him a jr drum kit, we ended up purchasing him a toy drum set--$20 at JC Penney--when he was two which he was thrilled with! He combined it with his "tin set" and banged away on it regularly for two years. Our feeling was that it was a MUCH less expensive way to go initially and a way for us to gage the interest/longevity level. We could always trade up later. Which we did. At 4, we bought him a real drum kit (jr size) which he continues to play regularly. He'll be eight in a few weeks. He is already talking about that full size kit someday. Yikes! (We're thinking when he's 10).
Our approach was this: the interest and drive were clearly there. Although there are times when he takes a break for weeks or even months... he always comes back around to it and plays regularly for months (sometimes hours a day). The pattern has been consistent since he was about 1 years old. OTOH, DH and I wanted to give unconditionally and told ourselves that if he loses interest that's ok too. Well, he hasn't lost interest and it would be hard to imagine how this would happen, but even if so, that would be ok. Our feeling is, it's never a bad idea to have good instruments around the house.
Of course... we're both musicians so...
The best in whatever you decide.