Thanks! A lifetime of sunblock and gentle washing will get you a long way with skin - treat it well, it's the only skin you get.
The reason that the large cosmetic companies usually only head up into the 30s with foundation is that you have to be able to have a reasonable application. SPF will vary if you apply the foundation more lightly or more heavily than another user. The SPF rating you see on the bottle is based on a medium-to-heavy application. If you're applying your sunscreen or sunblock (chemicals are sunscreen, minerals are sunblock - one filters, the other physically blocks the sun's rays) as a separate step, you get to determine how much you apply.
I burn very, very quickly - as you can see, I'm very pale. Additionally, I have a skin condition and take a medication for a genetic autoimmune disease that makes me more prone to burning. My average time in the sun to a burn on a partially-cloudy day in the summer in my area, as timed by my dermatologist, is about three to four minutes. This means that with SPF 30 sunblock on, I can be in the sun about 90 to 120 minutes. SPF is a multiplier for the time you can be outside from the normal time you burn. (Take the time it takes you to burn x SPF = Time outside with that product) To be safe in the summer, SPF40 gets me 120 to 160 minutes - which takes me to the two hour reapplication mark most producers suggest.
Also keep in mind that no sunscreen on the market will advise you to stay in the sun with it on longer than 2 hours (or 120 minutes) without reapplying. Sweat, water, and transfer can all take off your sunscreen/block. SPF ratings above 45 or so have been shown in a few different studies to be inaccurate, faulty, or downright fraudulent. You are better off getting a tinted moisturizer and reapplying your sunscreen and touching up your makeup through the day than you are trying to go with an SPF 60, 70, or higher product. I do have very high SPF sunblock (I have some that range from 50 to 120) that I use for days at the beach, on the water, in the snow, and other high-UV environments - there's a place for these products but daily use isn't really it. When you're using sunscreen, you should also be putting it on places you don't usually put your foundation - the back of your neck, the tops of your hands, your arms, the tops of your feet if you're wearing sandals and your legs if you're wearing shorts or a skirt, the tops of your ears and a million other places. So, you're not really doubling up on products anyway!
So, do I think you need the highest SPF foundation? No. I think you need one that's going to work with your skin, especially at your age. You want something free of parabens, light on coverage (or buildable - odds are good you don't need a full-coverage right out of the gate,) and breathable. Worry about color matching and coverage, then worry about SPF - you can always do SPF separately.
Before buying any foundation, I suggest visiting your local Sephora (if you have one) and your local high-end department store (Macy's, Dillards, Nordstrom, Bloomingdales, whatever you have in your area) and visiting a few counters. Tell them you're new to make up and are looking to try a few things. Don't be afraid to ask for samples but don't be shocked if they say no - it helps you ask for specific samples ("I was wondering if you could help match me to a foundation and send me home with a sample to try applying myself at home before I buy it?") If you are not intending to buy anything that day, don't take up the time of a sales representative when there is someone else at the counter - ask if you can look around while they help the other customer and help you when they're less busy. Visit your local MAC counter on a day when they're not busy - most of the folks that work at MAC love makeup and fun looks and are happy to show new folks how to apply. The catch with visiting a counter is that a purchase is implied if you get assistance applying product or learning a new technique - make sure to tell them up front if you're not buying today. If you get a rude employee, don't be afraid to look for another one - it's nothing about you, personally, I've been blown off by dozens of makeup counter sales folks when I was intending to drop hundreds of dollars that day - even at MAC. You never know why you've been blown off - a bad day for the employee, a sale that went south, or a general attitude issue; it's better to just move on to someone who will help you or come back another day than to worry too much about it.
Sephora is a lot more of a relaxed environment where customers are encouraged to (cleanly! If you don't know how, ask an employee! They have swabs and applicators to use) test products - personally, I never use a Sephora tester on my face but on the back of my hand or the inside of my arm, no problem. At the same time, they don't have everything a high-end counter is going to have and the store employees are more likely to be retail folks than makeup pros (or highly invested hobbyists,) in addition to carrying a dizzying array of products it's hard to be fully knowledgeable on, so you're more on your own in a Sephora than you would be at, say, a MAC counter.
