You're in your 20s, just graduated medical school and have started your internship. You've got medical school loans, rent, credit cards, and assorted bills to pay. Why think about retirement now? Because saving now means safeguarding your retirement later.
Time is your best friend. If you start at age 25 and invest $1000 per year in a tax-deferred account that earns 7% a year, you'll have accumulated $199,635 by age 65. The same amount invested every year starting at age 40 will only earn you $63,249 at age 65. If there is a 401(k) available to you, jump in as soon as possible and make sure to get the full company-match benefit. That's free money working for you. If you leave your company, be sure to carry that 401(k) over to an IRA, so it can continue to grow.
Most important, be proactive now. Contact an investment advisor and plan ahead. If you set aside as much as you can now, you can avoid investing more of your income later in life, when you may need it most.