My thoughts - it would be
poor money management making one large payment into your mortgage. Your lender is correct - it will shorten your term. Not knowing your financial situation, do you have other debt you can pay off? Also not knowing your LTV ratio, interest rate, or current loan terms. You could consider buying down your mortgage balance and do a stream-line (in house) refinance with your exisitng lender. A shorter term, a lower interest rate, possible a lower payment.
Noting a stream line refinance is your staying with your same lender, refinancing with little to no closing costs. Unless you have an extremely high interest rate, I do not recommend refinancing with another mortgage lender because of the cost in equity. Many people are talked into the benefits of lowering interest rate, not relizing what it will cost them. Further compearing the drop in the "Net Effective Increase Rate" by sending extra applied to principle, compeared to the closing costs of a new loan. Again we do not know your current situation with your existing loan.
Another veiw - have you considered investing in yourself?
- Sending one large payment does nothing for you credit score. By sending extra with your normal payment for 6 to 8 months and continuing, you're reported as more responsible. As a reward your credit score dramatically shoots up. It's not rocket science to understand having a high credit score you 100% pay less in life, contrary with a low credit score you 100% pay more...
- Have you considered education? Again investing in yourself to increase your knowledgeand make yourself more marketable? So there is more income for your future..: The Future is so bright...
- Savings - many people talk about the importance of a 401K, which is taxed defurred when making a deposit. Then taxed when you retire. The problem with that situation comparing how the taxes raise every year. It is almost predictable you could be paying more in taxes when you do retire. Another option to look at is Muni's which over time grow tax free...
- You have a job, which you receive earned income. When your younger it is a fact there are more opportunitys compared to when you are older. Have you considered creating a portfilio of yourself looking at investing so you have residual income for your future?..
The last 12 years have worked with 1000's either looking to pay less, or save what they have.
- The individuals with better money management skills have more opportunitys and a better quality of life.
Good Luck