No, your age is not a factor at all 
your age will not factor in... what will is:
1. Amount of debt to income (including the house payment).... what price range are you looking for?
2. Down payment will need to be at least 5% of the loan (unless you look at FHA which is 3.5%, or USDA, which is $0 down, but only in rural areas, etc)
On top of your down payment, you will need closing costs (estimate 3% on average, however there's always ways around this )
On top of down payment and closing costs, you will most likely need reserves (estimate 2-6 months PITI (principle, interest, tax, insurance + any mortgage insurance and association fees) -- this isn't an issue if you finance FHA... however 401k, stocks, etc... can be used at a value of 60% to cover these if needed.
I would say that right now, with your income (and stated debt) you *might* qualify for up to a $2400/month mortgage (basing total DTI at 30%, as I'm not sure what it is for single mortgage holders)
As long as your credit scores are over 640 you shouldn't have too much of problem qualifying (620 with FHA)
Not sure what city/county you live in, but FHA has caps on the amount it will loan. In my county in MN, the cap is $318,500. You should find out... as that will be your MAX loan amount that you can get FHA. If you use my county's cap ($318,500), that would put you at a MAX of $333,500 (if you have a $15,000 down payment). You shouldn't need reserves. However, if you want to go over the FHA max, that money needs to come out of your pocket as part of your down payment. Meaning, if you wnat a $425,000 house, and the FHA max is $318,500... you're looking at a $106,500 down payment to get into the loan. I would suggest you look up your county and get the FHA limit for it. Then at least you know what you're max is... and what kind of down payment you need to go above it
I do believe that when I had them hard pull for the approval I dropped about 5 pts. Nothing major. And if you do your shopping around within the same week, the inquiries will all be combined and won't individually hit you. Meaning if you applied at 5 placed, your CR might reflect 5 hard pulls, but you won't be hit with a 25 pts decrease
If you know your FICO scores, my recommendation would be to start talking to Mortgage Brokers... not individual lenders. A mortgage broker can offer you access to a lot of different products that may not be offered at specific banks, etc.
I forgot... FHA required me to put down either 6 months (or a year... can't rememer) escrows. So that's PMI, taxes and home owners insurance... and any association fees you have escrowed. So you will want to ask about that as well
One thing... if you're not in a huge hurry, I would recommend getting scores to a 640 minimum across the board as it will open up a LOT of options for you. You could do higher conventional mortgage options with 5% down, vs being limited to the FHA max amount. ..... and FHA PMI is REALLLLLYYYYYYY high!!!!!
Also, sorry.. I didn't answer your last question. About the risk of pre-qualifying with one lender and using a different one.
If you are looking to build, you will NEED a pre-qualification letter from your lender. Most new construction builders won't even move forward without it.
Also, if you are not looking to buy a home that is already built by a new construction builder, find out how much they require down to start build. There are a LOT of builders out there who won't work with people who don't have at least 10% down before build starts
My last thought... most builders work with one or more mortgage brokers. Find the builder you like, and trust... and talk to his broker. You will want to find a broker on your own as well... just to make sure that you're not getting railroaded into anything that profits either of them, and puts you in a hole to start with
I'm going through the building process myself right now (third time) and can answer any questions you might have Just drop me an email!!
Great advice. I live in MD, the counties I am looking in, FHA max out between $494,500 - $625,500 for single family. Thanks for recommending to use a mortgage broker. This is very helpful information. Thanks!!!!