Op Amp Output having oscillation
1) Your most likely culprit is the ground connection on pin 4 of the LT6200. That skinny trace is just asking for trouble. Make a via to ground right at the pin.

2) Your decoupling caps likewise. A via for each. And R29/C40, too.

3) Your R23/R24 combination will produce an effective input impedance of 20 ohms, assuming the LT6200 is working correctly. This will not cause oscillation, but it does represent a gross impedance mismatch to your presumed 50 ohm signal.

ETA - Point 3 applies to AC components only. DC doesn't count since it is blocked by C35.