If you have two strikes any felony can be a third. However, we can file a Romero motion to "strike" one or both of the strikes, particularly if they are old or from another state. If you are convicted of a third strike you will get 25 year to life. Therefore, we fight these cases "tooth and nail".
In California, first and second strikes are counted by individual charges, rather than individual cases, so a defendant may have been charged and convicted of "first and second strikes", potentially many more than two such strikes, arising from a single case, even one that was disposed of prior to the passage of the law.
Convictions from all 50 states and the Federal courts at any point in the defendant's past, as well as juvenile offenses that would othenwise be sealed can be counted (although once a juvenile record is sealed, it cannot be "unsealed"; it does not exist any longer and there is no longer any record to be used as a prior conviction), regardless of the date of conviction or whether the conviction was the result of a plea bargain.
Defendants already convicted of two or more "strike" charges arising from one single case potentially years in the past, even if the defendant was a juvenile at the time, can be and have been charged and convicted with a third strike for any felony or any offense that could be charged as a felony (including "felony petty theft" or possession of a controlled substance prior to Proposition 36 and given 25 years to life. (In the California Supreme Court decision People vs. Garcia, the Court withdrew residential burglary from the juvenile strike list.
For a juvenile residential burglary to count it must also be adjudicated in combination with another felony such as armed robbery, which is a strike. Out of the over 43,000 second and third strikers in California prisons today, none has received a prior strike for residential burglary as a juvenile.)