If you told me this eight years ago, it would have been enws to me.
Seriously though - it's not recommended. Any other pok�mon you catch will seem to grow at snails' pace compared to your starters, unless you play through both games at the same time (which is no fun - repeating yourself is extremely tedious) and trade each pok�mon you catch. Why would you want a Squirtle anyway?
Since all three starters have nice alternatives, there's no need to do this:
Ninetales is a decent alternative to Charizard.
Vileplume is a great alternative to Venusaur, and Victreebell is pretty good too.
Vaporeon and Poliwrath are both a lot better than Blastoise will ever hope to be.
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